* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-09-03 7:35 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-09-03 7:35 UTC (permalink / raw)
To: lwn, cwn, caml-list
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Hello
Here is the latest OCaml Weekly News, for the week of August 27 to
September 03, 2019.
Table of Contents
─────────────────
Ocaml-multicore: report on a June 2018 development meeting in
Paris
Interesting OCaml Articles
Old CWN
Ocaml-multicore: report on a June 2018 development meeting in
Paris
═══════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ocaml-multicore-report-on-a-june-2018-development-meeting-in-paris/2202/10>
Deep in this thread, sid announced
──────────────────────────────────
As a small step towards multicore, its interesting to note that
<https://github.com/ocaml/ocaml/pull/8713> just got merged to
master!
Interesting OCaml Articles
══════════════════════════
Archive:
<https://discuss.ocaml.org/t/interesting-ocaml-articles/1867/46>
Yotam Barnoy announced
──────────────────────
<https://www.ocamlpro.com/2019/08/30/ocamlpros-compiler-team-work-update/>
Old CWN
═══════
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-10-15 7:28 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-10-15 7:28 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 5627 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of October 08
to 15,
2019.
Table of Contents
─────────────────
capnp-rpc 0.4.0
Ocaml-protoc.plugin.1.0.0
Old CWN
capnp-rpc 0.4.0
═══════════════
Archive:
<https://discuss.ocaml.org/t/ann-capnp-rpc-0-4-0/4524/1>
Thomas Leonard announced
────────────────────────
I'm pleased to announce the release of [capnp-rpc 0.4.0], an
OCaml
implementation of the Cap'n Proto RPC specification.
If you haven't used the library before, please see the
[documentation
and tutorial]. Cap'n Proto RPC aims to provide secure,
efficient,
typed communications between multiple parties.
This library is now being used to build [ocaml-ci], where it is
used
for all communication between the web frontend and backend
services,
and to provide a command-line client.
[capnp-rpc 0.4.0]
<https://github.com/mirage/capnp-rpc/releases/tag/v0.4.0>
[documentation and tutorial]
<https://github.com/mirage/capnp-rpc/blob/master/README.md>
[ocaml-ci] <https://github.com/ocaml-ci/ocaml-ci>
Main changes since v0.3
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
Breaking changes:
• Wrap errors with the ``Capnp' tag to make it easier to compose
with
other types of error.
• Prefix all command-line options with `capnp-'.
e.g. `--listen-address' is now `--capnp-listen-address'. The
old
names were confusing for applications that supported other
protocols
too (e.g. a web server).
New features:
• Add `Capability.with_ref' convenience function. This
automatically
calls `dec_ref' when done.
• Add Unix `Cap_file' module to load and save `Sturdy_refs'. In
particular, this ensures that saved cap files get a mode of
`0o600',
since they contain secrets.
• Export cmdliner network address parsing. This is useful if
you
don't want to use the default option parsing. For example, if
you
want to make Cap'n Proto an optional feature of your program.
• Upgrade from `uint' (which is deprecated) to the newer
`stdint'.
The latest version of `uint' is just a wrapper around
`stdint', so
this shouldn't break anything if you are using the latest
version.
• Put cmdliner options in their own man-page section. Use
`Capnp_rpc_unix.manpage_capnp_options' to control where in
your
man-page they appear.
• Enable `SO_KEEPALIVE' for TCP connections. For use with
Docker's
libnetwork, try something like this in your `stack.yml':
┌────
│ sysctls:
│ - 'net.ipv4.tcp_keepalive_time=60'
└────
Ocaml-protoc.plugin.1.0.0
═════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-ocaml-protoc-plugin-1-0-0/4535/1>
Anders Fugmann announced
────────────────────────
I'm happy to announce the second release of
[ocaml-protoc-plugin].
Ocaml-protoc-plugin is a plugin to googles `protoc' compiler
which
generates type idiomatic to ocaml from `.proto' files including
full
compliant serialization and deserialization functions.
[ocaml-protoc-plugin]
<https://github.com/issuu/ocaml-protoc-plugin>
Most noteworthy changes in this release:
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
• Full proto2 support.
• The list of dependencies has been slimmed way down, and now
only
depends on `conf-protoc' (the `protoc' compiler and googles
*well
known types*).
• Buckescript support.
• Added options to change the ocaml (type for scalar types (int,
int64
or int32).
Many thanks to Wojtek Czekalski for helping trimming
dependencies and
for Buclescript support.
Full changelog:
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
• Support enum aliasing
• Avoid name clash with on 'name'
• Fix code generation when argument contains a path
• Refactor internal types to make serialization and
deserialization
type spec symmetrical.
• Optimize deserialization for messages with max_id < 1024
• Don't depend on Base in runtime
• Slim runtime dependencies: Remove need for base, ocplib-endian
and
ppx_let
• Honor [packed=…] flag.
• Make fixed scalar types default to int32 and int64
• Support proto2 specification
• Add options to switch between int64|int32 and int
• Fix name clash problem with special enum names
• Refactor serialization and deserialization to simplify emitted
code
• Eagerly evaluate serialization (for speed).
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
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[Alan Schmitt]
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[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-11-05 6:55 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-11-05 6:55 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 1700 bytes --]
Here is the latest OCaml Weekly News, for the week of October 29
to
November 05, 2019.
Table of Contents
─────────────────
vim-ocaml - new home
Old CWN
vim-ocaml - new home
════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-vim-ocaml-new-home/4615/1>
Rudi Grinberg announced
───────────────────────
Dear Vim & Neovim users,
I would like to announce that I've officially moved the
[vim-ocaml]
repository under the control of the OCaml organization on
github. Please direct your bug reports and pull requests to this
repository. This move is done not because vim-ocaml is being
neglected, on the contrary, there's an active team of
maintainers that
recently expanded. I simply want to take this opportunity to
draw more
Vim & Noevim users to this project, as I suspect many users
aren't
aware of recent efforts.
[vim-ocaml] <https://github.com/ocaml/vim-ocaml>
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
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[Alan Schmitt]
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-11-12 13:21 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-11-12 13:21 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 2875 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of November 05
to 12,
2019.
Table of Contents
─────────────────
Mirage 3.7.1 released
Old CWN
Mirage 3.7.1 released
═════════════════════
Archive:
<https://discuss.ocaml.org/t/mirage-3-7-1-released/4634/1>
Hannes Mehnert announced
────────────────────────
MirageOS 3.7.1 is released to opam repository now.
Breaking change:
• The hooks previously defined in
OS.Main.at_enter/at_enter_iter/at_exit/at_exit_iter are now
part of
Mirage_runtime (only used by mirage-entropy)
<https://github.com/mirage/mirage/pull/1010>
Behaviour changes of MirageOS unikernels:
• A unikernel now always calls the Mirage_runtime.at_exit
registered
hooks – once a unikernel succesfully executed its `start' in
`Lwt_main.run', `exit 0' is called to ensure this behaviour
<https://github.com/mirage/mirage/pull/1011>
• Top-level exceptions are no longer caught (there used to be in
mirage-unix/mirage-xen/mirage-solo5 custom handlers). The
OCaml
runtime prints the exception and backtrace on stdout and calls
exit
2 (from 4.10.0, abort() will be called).
Deprecations (being removed from Mirage 4.0)
• All Mirage_YYY_lwt are deprecated, Mirage_YYY interfaces are
no
longer astracted over 'a io and buffer. This reduces the
amount of
opam packages - mirage-yyy-lwt are no longer part of the
release
(each mirage-yyy package provides a Mirage_yyy_lwt module for
backwards compatibility). Motivation was discussed in
<https://github.com/mirage/mirage/issues/1004>
• mirage-types and mirage-types-lwt are deprecated, please use
the
Mirage_YYY signatures directly instead.
Other observable changes
• `mirage configure' now deletes all exising opam files
Most reverse dependencies are already released to opam, have a
look at
<https://github.com/mirage/mirage/issues/1012> for progress (and
the
temporary <https://github.com/mirage/mirage-dev.git#easy> opam
overlay).
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
it to you, or go take a look at [the archive] or the [RSS feed
of the
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[Alan Schmitt]
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[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives]
<http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-11-26 8:33 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-11-26 8:33 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 28861 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of November 19
to 26,
2019.
Table of Contents
─────────────────
tiny_httpd 0.1
printbox.0.3
v0.13 release of Jane Street packages
opam2nix (v1)
GitHub Actions for OCaml / opam now available
OCurrent 0.1 (CI/CD pipeline eDSL)
New pages for OCaml API
Irmin 2.0.0 release
Tail cascade: a new indentation style for some OCaml constructs
Old CWN
tiny_httpd 0.1
══════════════
Archive: <https://discuss.ocaml.org/t/ann-tiny-httpd-0-1/4727/1>
Simon Cruanes announced
───────────────────────
Hello and good morning, I'm pleased to announce that
[tiny_httpd] 0.1
has been released and is on opam.
The goal is to emulate python's standard `http.server' by
providing a
0-dependencies, minimalist, simple HTTP server for embedding in
applications that are not primarily a website, with very basic
routing
(thanks to `Scanf'). A binary `http_of_dir' is also distributed
and
can be used to serve a directory, with optional upload of files.
[tiny_httpd] <https://github.com/c-cube/tiny_httpd>
printbox.0.3
════════════
Archive: <https://discuss.ocaml.org/t/ann-printbox-0-3/4731/1>
Simon Cruanes announced
───────────────────────
<https://aws1.discourse-cdn.com/standard11/uploads/ocaml/original/2X/8/8e7c55c5ab69c12f53a7862d2f84dd6e0cfc0dc0.png>
┌────
│ let b =
│ let open PrintBox in
│ PrintBox_unicode.setup();
│ frame @@ grid_l [
│ [text "subject"; text_with_style Style.bold "announce:
printbox 0.3"];
│ [text "explanation";
│ frame @@ text {|PrintBox is a library for rendering nested
tables,
│ trees, and similar structures in monospace text or
HTML.|}];
│ [text "github";
│ text_with_style Style.(bg_color Blue)
"https://github.com/c-cube/printbox/releases/tag/0.3"];
│ [text "contributors";
│ vlist_map (text_with_style Style.(fg_color Green))
["Simon"; "Guillaume"; "Matt"]];
│ [text "dependencies";
│ tree empty
│ [tree (text "mandatory")
│ [text "dune"; text "bytes"];
│ tree (text "optional")
│ [text "uutf"; text "uucp"; text "tyxml"]]];
│ [text "expected reaction"; text "🎉"];
│ ]
│
│ let () = print_endline @@ PrintBox_text.to_string b
└────
([actual link to the release])
[actual link to the release]
<https://github.com/c-cube/printbox/releases/tag/0.3>
v0.13 release of Jane Street packages
═════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-v0-13-release-of-jane-street-packages/4735/1>
Xavier Clerc announced
──────────────────────
We are pleased to announce the v0.13 release of Jane Street
packages!
This release comes with 14 new packages, and a number of fixes
and
enhancements. The documentation for this release is available on
our
website:
<https://ocaml.janestreet.com/ocaml-core/v0.13/doc/>
The remainder of this mail highlights the main changes since the
v0.12
release; we hope it will be useful to developers in the process
of
migrating to the new version. A comprehensive changelog is
available
at the end.
Notable changes
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
• Changed `Base', `Core_kernel', and `Core' functions to raise
`Not_found_s' instead of `Not_found'. `Hashtbl.find_exn' and
`Map.find_exn' now include the key in their error message.
• Changed `Core' and `Core_kernel' to export `int' comparison
rather
than polymorphic comparison.
• Removed the "robust" float comparison operators (`>.', `=.',
…)
from the default namespace.
• Replaced `sexp_*' types (`sexp_list', `sexp_option',
`sexp_opaque',
…) with preprocessor attributes (`[@sexp.list]',
`[@sexp.option]',
`[@sexp.opaque]', …).
• Changed `let%map' syntax from `let%map.Foo.Let_syntax' to
`let%map.Foo'.
• Added to `match%optional' support for specifying a path, so
you can
write `match%optional.Foo foo_option' rather than `let open
Foo.Optional_syntax in match%optional foo_option'.
• Improved `Base.Backtrace' so that it enables recording of
backtraces
in more situations, specifically when `OCAMLRUNPARAM' is
defined but
doesn't mention the backtrace flag, `b'.
• Added javascript support for `Zarith', `Bigint', `Bignum', and
`Bigdecimal'.
• Changed `Hashtbl.create''s default `size' from 128 to 0.
• Changed `Core_kernel.Command' so that all commands accept
double
dash flags: `--help', `--version', and `--build-info'.
New packages
╌╌╌╌╌╌╌╌╌╌╌╌
• async_udp (<https://github.com/janestreet/async_udp>): UDP
support
for Async.
• async_websocket
(<https://github.com/janestreet/async_websocket>): A
library that implements the websocket protocol on top of
Async.
• bonsai (<https://github.com/janestreet/bonsai>): A library for
building dynamic webapps, using Js_of_ocaml.
• postgres_async
(<https://github.com/janestreet/postgres_async>):
OCaml/async implementation of the postgres protocol (i.e.,
does not
use C-bindings to libpq).
• ppx_cold (<https://github.com/janestreet/ppx_cold>): Expands
`[@cold]' into `[@inline never][@specialise never][@local
never]'.
• ppx_pattern_bind
(<https://github.com/janestreet/ppx_pattern_bind>):
A ppx for writing fast incremental bind nodes in a pattern
match.
• ppx_python (<https://github.com/janestreet/ppx_python>):
`[@@deriving]' plugin to generate Python conversion functions.
• ppx_yojson_conv
(<https://github.com/janestreet/ppx_yojson_conv>):
`[@@deriving]' plugin to generate Yojson conversion functions.
• ppx_yojson_conv_lib
(<https://github.com/janestreet/ppx_yojson_conv_lib>): Runtime
lib
for `ppx_yojson_conv'.
• pythonlib (<https://github.com/janestreet/pythonlib>): A
library to
help writing wrappers around OCaml code for python.
• sexp_select (<https://github.com/janestreet/sexp_select>): A
library
to use CSS-style selectors to traverse sexp trees.
• timezone (<https://github.com/janestreet/timezone>): Time-zone
handling.
• toplevel_backend
(<https://github.com/janestreet/toplevel_backend>):
Shared backend for setting up toplevels.
• zarith_stubs_js
(<https://github.com/janestreet/zarith_stubs_js>):
Javascript stubs for the Zarith library.
Deprecations / Removals
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
`Async_kernel':
• Deprecated monadic `ignore' functions in favor of `ignore_m'.
`Base':
• Deleted `Array.replace' and `replace_all' functions, which
have been
deprecated since before the last public release.
• Deprecated `Result.ok_unit'; use `Ok ()'.
• Removed the `Monad' and `Applicative' interfaces' `all_ignore'
function; it was previously deprecated and replaced by
`all_unit'.
• Removed `List.dedup', which has been deprecated since 2017-04.
• Removed `String' mutation functions, which have been
deprecated in
favor of `Bytes' since 2017-10.
• Deprecated `Array.truncate', `Obj_array.unsafe_truncate', and
`Uniform_array.unsafe_truncate'.
• Deprecated `Sys.argv', which has been superseded by
`get_argv',
which is a function, reflecting the fact that `argv' can
change (as
of OCaml 4.09).
`Core_kernel':
• Removed `Core_kernel.Std', which had been deprecated for a
year.
• Deprecated type `Command.Spec.param' in favor of
`Command.Param.t'.
• Removed `Hashtbl' functions that had been deprecated for
years.
• Removed `Float.to_string_round_trippable', which has been
deprecated
in favor of `to_string' since 2017-04.
• Deprecated `Fqueue' functions where one should use `Fdeque'
instead:
`bot', `bot_exn', and `enqueue_top'.
• Deleted `Bus.unsubscribes', which will be obviated by a
performance
improvement to `Bus.unsubscribe'.
`Timing_wheel':
• Removed the `alarm_upper_bound' function, which has been
deprecated
for 6 months, and superseded by `max_allowed_alarm_time'.
Moves
╌╌╌╌╌
`Core_kernel':
• Moved `Bounded_int_table' to a standalone library.
• Moved the `Pool' and `Tuple_type' modules to a standalone
library,
`Tuple_pool'.
`Async_unix':
• Moved `Unix.Fd.replace' into a `Private' submodule.
Changelog
╌╌╌╌╌╌╌╌╌
Please visit
<https://discuss.ocaml.org/t/ann-v0-13-release-of-jane-street-packages/4735>
opam2nix (v1)
═════════════
Archive: <https://discuss.ocaml.org/t/ann-opam2nix-v1/4741/1>
Tim Cuthbertson announced
─────────────────────────
Anouncing opam2nix (v1)
[opam2nix] generates [nix] expressions from the [opam] OCaml
package
repository. It works similarly to [bundix], [node2nix], etc:
You run an (impure) command to resolve all transitive dependency
versions using the current opam repository, generating a .nix
file
that locks down the exact package sources and versions. Then
this file
can be imported to provide `buildInputs' for building your ocaml
project in nix.
*What is nix and why would I care?* Well, that's a long story
but the
headline benefits of nix are:
• reproducible builds (if it builds for me, it builds for you)
• stateless (you don't set up switches and then install
packages, each
expression specifies everything it needs, and anything you
don't
have is fetched/built on demand)
• language agnostic (takes care of non-ocaml dependencies)
It's sadly not a shallow learning curve, but those benefits are
hard
to find elsewhere, so I obviously think it's worthwhile. So if
you use
nix (or would like to), please give it a try and provide
feedback. I'll (slowly) start working on upstreaming it into
nixpkgs.
[opam2nix] <https://github.com/timbertson/opam2nix>
[nix] <https://nixos.org/>
[opam] <https://opam.ocaml.org/>
[bundix] <https://github.com/nix-community/bundix>
[node2nix] <https://github.com/svanderburg/node2nix>
GitHub Actions for OCaml / opam now available
═════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/github-actions-for-ocaml-opam-now-available/4745/1>
Anil Madhavapeddy announced
───────────────────────────
I was in the [GitHub Actions] beta program and forward ported my
code
to the latest version that just went public. It's a pretty
simple way
to get your OCaml code tested on Linux, macOS and Windows,
without
requiring an external CI service. The action attempts to
provide a
homogenous interface across all three operating systems, so
invoking
'opam' from subsequent actions should "just work".
You can find it here:
• In the GitHub Marketplace at
<https://github.com/marketplace/actions/setup-ocaml>
• Source code on <https://github.com/avsm/setup-ocaml/>
• Hello World usage on
<https://github.com/avsm/hello-world-action-ocaml>
• Usage in ocaml-yaml:
•
<https://github.com/avsm/ocaml-yaml/blob/master/.github/workflows/test.yml>
• An [example ocaml-yaml run]
This should be considered fairly experimental as GH Actions is
so new.
If you do use it, then consider [updating this issue with your
usage].
It does not current supporting caching yet, but is pretty fast
to
bootstrap (~4minutes).
It also doesn't have any higher level purpose other than to set
up an
opam environment, since most of the additional functionality
such as
revdeps testing is planned for addition to the [ocurrent DSL].
Nevertheless, this GH feature will hopefully be useful for
smaller
projects without a lot of computational requirements. Let me
know how
it goes!
Windows is currently supported through @fdopen's excellent fork
that
uses Cygwin. As Windows support is being mainlined into opam
itself
at the moment, I'm hoping that we will gradually move over to
that.
That should eventually remove the need for two separate
opam-repositories, so I won't be adding any features that are
Linux or
macOS-specific and do not work on the Cygwin version.
[GitHub Actions] <https://github.com/actions>
[example ocaml-yaml run]
<https://github.com/avsm/ocaml-yaml/runs/314055554>
[updating this issue with your usage]
<https://github.com/avsm/setup-ocaml/issues/4>
[ocurrent DSL]
<https://discuss.ocaml.org/t/ann-ocurrent-0-1-ci-cd-pipeline-edsl/4742/2>
OCurrent 0.1 (CI/CD pipeline eDSL)
══════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-ocurrent-0-1-ci-cd-pipeline-edsl/4742/1>
Thomas Leonard announced
────────────────────────
[OCurrent] 0.1 has just been released to opam-repository.
OCurrent is an OCaml eDSL intended for writing build/test/deploy
pipelines. It is being used as the engine for [ocaml-ci] and the
[docker-base-images] builder (used to build the OCaml Docker
images,
such as `ocurrent/opam:alpine-3.10-ocaml-4.08'). Other good uses
might
be building and redeploying a Docker service or a unikernel
whenever
its source repository changes. It can be run locally as a single
Unix
process.
An OCurrent pipeline is written as an OCaml program, but the
OCurrent
engine ensures that it is kept up-to-date by re-running stages
when
their inputs change. A web UI is available so you can view your
pipeline and see its current state.
OCurrent can statically analyse the pipelines before they have
run,
allowing it to run steps in parallel automatically and to
display the
whole pipeline. It does this using a light-weight alternative to
arrows, which doesn't require programming in an awkward
point-free
style. See [CI/CD Pipelines: Monad, Arrow or Dart?] for more
about
that.
The basic functionality can be extended using "plugins" (just
normal
OCaml libraries). Plugins are available for interacting with
Docker,
Git, GitHub and Slack. These are in separate packages
(e.g. `current_github') to avoid having the base package pull in
too
many dependencies).
There is also an optional Cap'n Proto RPC interface, in the
`current_rpc' opam package. This is used, for example, by
[citty] to
provide a TTY interface to ocaml-ci.
[The OCurrent wiki] contains examples, and documentation on the
various plugins.
Here's an example pipeline (from the base image builder):
<https://roscidus.com/blog/images/cicd/docker-base-images-thumb.png>
[OCurrent] <https://github.com/ocurrent/ocurrent>
[ocaml-ci] <https://github.com/ocurrent/ocaml-ci/>
[docker-base-images]
<https://github.com/ocurrent/docker-base-images>
[CI/CD Pipelines: Monad, Arrow or Dart?]
<https://roscidus.com/blog/blog/2019/11/14/cicd-pipelines/>
[citty] <https://github.com/ocurrent/citty>
[The OCurrent wiki] <https://github.com/ocurrent/ocurrent/wiki>
Anil Madhavapeddy then added
────────────────────────────
For those curious about the relation to the existing CI used in
opam-repository, then it is no coincidence that @talex5 is the
author
of both :-)
This DSL is the next iteration of the [datakit-ci], but
specialised to
be faster and simpler for extending with OCaml and more complex
workflows that our OCaml Platform tools need these days (like
ocamlformat linting, or dune expect promotion, or odoc
cross-referenced doc generation). We are planning a smooth
migration
next year over to the new system, but wanted to release this
early to
show you some of the pieces going into this new iteration. I am
particularly excited about the new tty-based interface that
saves an
awful lot of clicking around on web UIs for CI results…
[datakit-ci] <https://github.com/moby/datakit>
New pages for OCaml API
═══════════════════════
Archive:
<https://discuss.ocaml.org/t/new-pages-for-ocaml-api/4720/13>
Continuing this thread, sanette announced
─────────────────────────────────────────
I have uploaded a new version (same link
<https://sanette.github.io/ocaml-api/>)
• background color for links in the TOC @Maelan
• more indentation for value descriptions @Maelan, @grayswandyr
• word wrapping long `<pre>' codes @grayswandyr
• type table: remove `(*' and `*)', give more space to code wrt
comments, diminish comment's color @grayswandyr
searching is not ready yet… please wait suggestions for dark
theme
welcome
sanette later added
───────────────────
I have just uploaded a new version with a basic search engine.
• for each page, you can search values/modules
• in the general index page, the search includes also the
descriptions
• search results are ranked by relevance
the downside is that each page now comes with an index of about
570Kb
in the form of an index.js file. I'm kind of hoping that the
browser
will cache this, but I'm not sure. It would be maybe better to
only
load the index file on demand.
Irmin 2.0.0 release
═══════════════════
Archive:
<https://discuss.ocaml.org/t/ann-irmin-2-0-0-release/4746/1>
Thomas Gazagnaire announced
───────────────────────────
On behalf of the Irmin development team, I am very happy to
announce
the release of Irmin 2.0.0, a major release of the Git-like
distributed branching and storage substrate that underpins
[MirageOS]. We began the release process for all the components
that
make up Irmin [back in May 2019], and there have been close to
1000
commits since Irmin 1.4.0 released back in June 2018. To
celebrate
this milestone, we have a new logo and opened a dedicated
website:
[irmin.org].
More details here:
<https://tarides.com/blog/2019-11-21-irmin-v2>
[MirageOS] <https://mirage.io/>
[back in May 2019]
<https://tarides.com/blog/2019-05-13-on-the-road-to-irmin-v2>
[irmin.org] <https://irmin.org/>
Tail cascade: a new indentation style for some OCaml constructs
═══════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/tail-cascade-a-new-indentation-style-for-some-ocaml-constructs/4736/1>
gasche announced
────────────────
I recently decided to change my indentation style for certain
OCaml
constructs in a way that I'm going to describe below. I just
coined a
name for this approach, "tail cascade". I'm creating this topic
to
convince everyone that this is a cool idea you should adopt as
well. Or at least tolerate it when you review other people's
code.
Problem
╌╌╌╌╌╌╌
Programs that heavily use `match' often see a shift to the right
due
to nested indentation.
┌────
│ match foo with
│ | Foo -> ...
│ | Bar x ->
│ match bar x with
│ | FooBar -> ...
│ | Blah y ->
│ match f y with
│ | Some z ->
│ ...
└────
Another problem with this style is that it suffers from the
"dangling
bar" issue: if you try to add a new case for one of the exterior
`match', it is parsed as belonging to the innermost `match'.
People
have been recommending (rightly) to use `begin match .. end' for
all
nested match constructs to avoid this issue.
┌────
│ match foo with
│ | Foo -> ...
│ | Bar x ->
│ begin match bar x with
│ | FooBar -> ...
│ | Blah y ->
│ begin match f y with
│ | None -> ...
│ | Some z ->
│ ...
│ end
│ (* now this is safe *)
│ | FooBlah -> ...
│ end
└────
But still the unpleasant shift to the right remains.
Proposal: cascading tail case
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
We should in general use `begin match .. end' for nested
matches. But
the "cascading tail case" proposal is to *not* do it for the
*last*
case of the pattern-matching, and instead *de-indent* (dedent)
this
last case – tail case.
┌────
│ match foo with
│ | Foo -> ...
│ | Bar x ->
│ match bar x with
│ | FooBar -> ...
│ | Blah y ->
│ match f y with
│ | None -> ...
│ | Some z ->
│ ...
└────
Note that with this indentation style, the "dangling match"
problem is
also avoided: unlike with the original, non `end'-protected
program,
the indentation makes it immediately obvious that any further
case
will be attached to the innermost match, and not any of the
exterior
ones.
A program using this "cascading tail" approach should always use
`begin match .. end' for nested matches, except for a nested
match
returned within the last branch of an outer match, which can
(optionally) be dedented instead.
The choice to dedent the last case corresponds to encouraging a
sequential reading of the program, where the other cases are
"auxiliary cases" checked first and dispatched quickly, and the
last
case is the "main part" where the "rest" of the logic of the
program
lies. This pattern is typical of nested pattern-matching on the
`option' or `result' type for example:
┌────
│ match foo x with
│ | Error err ->
│ fail_foo_error err
│ | Ok y ->
│ match bar y with
│ | Error err ->
│ fail_bar_error err
│ | Ok () ->
│ ...
└────
Remark: it is *not* always the case that the `Error' constructor
is
the auxiliary case, and the `Ok' constructor is the main case;
sometimes we implement fallback logic like "if `foo' work then
we are
good, but otherwise we have to do this and that", and the error
case
is the most salient (and longer) part of the program logic. I
would
recommend being mindful, when you write code, of whether there
is a
most convincing way to "sequentialize" it (distinguish auxiliary
and
main/tail case), and avoid using cascading tails when there is
no
clear sequentialization choice.
Remark: some cases of tail cascades can be linearized by using a
good
definition of "bind" and a monadic style. This tends to be very
limited however: it fixes one of the constructors to always be
the
"tail" constructor (always `Some', always `Ok'), and it only
works
when the handling of the other constructors is very homogeneous
(typically: return directly). In real code, many situations
occur
where the monadic style doesn't fit the problem, but tail
cascade does
help writing a readable program.
Generalization: tail cascade
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌
While I have never seen cascading tail cases in real-world OCaml
code
before (I'm happy to be given pointers; I think that the idea is
not
new, but I'm not aware of previous attempts to give it a catchy
name
and spread the cascade love), this is in fact a new (to me)
instance
of a common technique that is used for other OCaml constructs:
┌────
│ if foo x then ...
│ else if bar x then ...
│ else ... (* this `tail else` was dedented *)
│
│ let x = foo in
│ let y = bar in (* this `tail let` was dedented *)
│ ... (* and the rest as well *)
│
│ bind foo @@ fun x ->
│ bind bar @@ fun y -> (* this "tail function body" was dedented
*)
│ ... (* and the rest as well *)
└────
I would call "tail cascade" (or maybe: "cascading tail") the
idea of
dedenting the "rest" of an OCaml expression (compared to a
strict
tree-nesting-based approach) when it morally describes the
"rest" of
the expression. I use the name "tail" because those expressions
are
almost always in tail-position in the sense of tail-calls.
This general approach legitimizes some styles that I have seen,
and
sometimes used, in the wild, while at the same time considering
that I
may have been doing something improper, for example:
┌────
│ if foo then blah else
│ ... (* dedented *)
│
│
│ Fun.protect
│ ~finally:(...)
│ @@ fun () ->
│ ... (* dedented *)
│
│
│ try simple_approach with exn ->
│ ... (* dedented *)
│
│
│ 1 +
│ 2 + (* dedented *)
│ ... (* dedented *)
└────
Remark: after a `then' or `else', many people share the
reasonable
view that any expression containing imperative constructs (`foo;
bar')
should be enclosed in a `begin .. end' block to avoid
surprising-precedence issue. Just as for nested `match', this
recommendation should be lifted for "tail else" constructs.
Remark: The last example is a case where the dedented
expressions are
*not* in tail-position from a runtime-evaluation point of view.
I am
not sure as whether the two notions should be made to coincide
more
strongly, but in any case I'm not fond of the style in this
particular
example, I prefer to move the infix operator to the beginning of
the
next line instead, following a different style and
justification.
The possibility this "cascading tail" style today crucially
relies on
the nesting properties of open-ended syntactic constructs,
notably
`let' (commonly cascaded), and now `match' and `if
... else'. Proposals to transition to a syntax where `match' and
`else' are forced to take a closing marker are incompatible with
the
cascading style. I have not made my mind on whether this should
be
considered a blocker for those proposals, but at least it shows
that
having the open-ended form available has value for certain
programs.
Louis Gesbert then said
───────────────────────
@gasche I prototyped a dedicated option in `ocp-indent', if
you're
interested in trying it out :)
┌────
│ opam pin
git+https://github.com/OCamlPro/ocp-indent#match-tail-cascade
│ echo "match_tail_cascade=true" >> ~/.ocp-indent
└────
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
it to you, or go take a look at [the archive] or the [RSS feed
of the
archives].
If you also wish to receive it every week by mail, you may
subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives]
<http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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^ permalink raw reply [flat|nested] 12+ messages in thread
* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-12-03 15:43 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-12-03 15:43 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 22620 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of November 26
to
December 03, 2019.
Table of Contents
─────────────────
Irmin 2.0.0 release
How viable is delivering binaries linked to Cygwin to Windows
customers?
Dune 2.0.0
Advanced C binding using ocaml-ctypes and dune
Upcoming breaking change in Base/Core v0.14
CI/CD Pipelines: Monad, Arrow or Dart?
Use of functors to approximate F# statically resolved type
parameters
Old CWN
Irmin 2.0.0 release
═══════════════════
Archive:
<https://discuss.ocaml.org/t/ann-irmin-2-0-0-release/4746/5>
Continuing this thread, samoht announced
────────────────────────────────────────
And there is now a follow-up blog post, explaining how to use
the new
GraphQL API available in Irmin2:
<https://tarides.com/blog/2019-11-27-introducing-irmin-graphql>.
How viable is delivering binaries linked to Cygwin to Windows
customers?
════════════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/how-viable-is-delivering-binaries-linked-to-cygwin-to-windows-customers/4775>
mbacarella asked
────────────────
I’m in the early stages of planning a deliverable binary product
that
will run on Linux, Mac and Windows.
My brief sniff of the air around the OCaml ecosystem says I
should
expect to target Cygwin to get Windows going (although there’s
impressive work to get native Windows stuff done that can become
the
preferred approach in a few years).
My experience using Cygwin as an operating environment is that
it’s
pretty darn sluggish compared to Linux on the same computer.
Why is this? There’s an anecdote that says Cygwin can only fork
at
about 30-50x a second on Windows, due to how it has to adapt it
to
work within Windows’ task spawning model. (For contrast, Linux
can
achieve thousands of forks per second if you play around with
it).
I understand from another product developer that when they build
binaries to deliver to Windows/Cygwin, they actually
cross-compile on
Linux because of how slowly the toolchain runs on Cygwin.
That sounds like bad news if you want to do UNIXy things, but
for a
single standalone application this might not be so bad? I assume
if I
ship a deliverable to Windows/Cygwin, the end user may enjoy
good
performance, so long as I’m not spawning tons of processes or
relying
on fork for multi-programming. Is this a safe assumptions?
Any other gotchas when it comes to OCaml on Cygwin w.r.t.
performance?
The app pretty much has real-time gaming requirements (though
it’s not
a game so can side-step worrying about access to GPUs and
what-not). Stated another way, although my application will
depend on
the POSIX layer offered by Cygwin, I expect it not to crunch
POSIX
related stuff in the main loop.
How has your experience gone?
John Whitington replied
───────────────────────
I have been shipping commercial binaries for Linux (32 and 64
bit),
Windows (32 and 64bit) and OS X for years. For example:
<https://github.com/coherentgraphics/cpdf-binaries>
And even static or shared libraries in binary form:
<https://github.com/coherentgraphics/cpdflib-binary>
On OS X, you need to use MACOSX_DEPLOYMENT_TARGET or similar to
make
sure your builds will run on older systems. And, in fact, you
need to
use MACOSX_DEPLOYMENT_TARGET when asking OPAM to compile the
OCaml
compiler itself. And, you will need to deal with codesigning and
notarization. But it’s all doable.
For linux, you may need to build under older linux versions, to
make
sure that the glibc in use is old enough. This is not an
ocaml-specific problem. I have a 64 bit and 32 bit VM with
old-ish
glibc versions for this purpose.
Under Windows, there are no such backward-compatibility
problems. I
use the new OCaml for windows system, which comes with OPAM, and
is
mingw-based. No cygwin remains in the final binary.
For more obscure systems (AIX, HPUX, Sparc etc) customers
compile from
source (with help from me). Not once in more than ten years has
anyone
cared that it was written in OCaml.
dbuenzli also replied
─────────────────────
remember that on the Windows native port, the Unix module
distributed
with OCaml is your POSIX compatibility layer. There are a few
entry
points to avoid though, the list is at the bottom of [this
page].
[this page]
<https://caml.inria.fr/pub/docs/manual-ocaml/libunix.html>
nojb also replied
─────────────────
At LexiFi our main application is developed and shipped on
Windows. We
use the msvc port of OCaml. This means that you need Cygwin to
develop, but the resulting application is fully native and does
not
depend on the Cygwin DLL. As @dbuenzli mentioned, the Unix
module *is*
the POSIX compatibility layer.
Compilation speed is slower on Windows because process creation
is
slower on Windows as a general rule, but it is manageable (our
application has around 2000 modules + Js_of_ocaml + C bindings +
C#
component).
We don’t have any issues with runtime performance. The `Unix'
library
mentioned above implements Windows support directly without
going
through any compatibility layer and is quite efficient.
BikalGurung also replied
────────────────────────
There is an editor being built in ocaml/reasonml which currently
targets windows, linux and macos -
<https://github.com/onivim/oni2>. However, the binary is native
windows rather than cygwin derivative. So if you don’t have to
use
cygwin dependencies then native windows binary could be the way
to go.
Also esy - <https://github.com/esy/esy> makes developing
ocaml/reasonml on windows viable.
keleshev also replied
─────────────────────
*TLDR*: Install the [Mingw port of OCaml 4], freely use most
opam
libraries, and compile to native Windows binaries, without
licensing
issues.
I recommend you read the “Release notes for Windows”:
<https://github.com/ocaml/ocaml/blob/trunk/README.win32.adoc>
To summarise, there are three Windows ports:
• Native Microsoft port,
• Native Mingw port,
• Cygwin port.
All three require Cygwin for development purposes. I recommend
using
the Native Mingw, as:
• it *doesn’t* require Visual Studio (it uses a mingw fork of
GCC that
“cross-compiles” native Windows executables),
• it *doesn’t* rely on the dreaded cygwin.dll
• it has good opam support with opam-repository-mingw:
<https://github.com/fdopen/opam-repository-mingw>
• it has a convenient installer:
<https://fdopen.github.io/opam-repository-mingw/> 5.
To contrast, Native Microsoft requires Visual Studio, and
doesn’t have
opam. You can still vendor pure OCaml packages, but as soon as
you
want to use some C bindings you’re in trouble, because of the
“minor”
differences between Visual C and GCC. And everything assumes GCC
nowadays.
Cygwin port is the one I don’t have experience with, but
re-reading
the “Release notes for Windows” above it strikes me that it
mentions
that Cygwin was re-licensed from GPL to LGPL with static linking
exception. So it looks like the Cygwin port could be viable for
commercial use, but I never tried to statically linked
`cygwin.dll',
and I’m not sure what are the benefits of Cygwin port over the
Mingw
port.
[Mingw port of OCaml 4]
<https://fdopen.github.io/opam-repository-mingw/>
dmbaturin also replied
──────────────────────
With [soupault 4], I decided to ship prebuilt binaries for all
platforms including Windows. Mostly to see if I can, all its
users I
know of are on UNIX-like systems and know how to build from
source,
but that’s beside the point. :wink:
I can confirm everything @keleshev says: fdopen’s package just
works,
opam works exactly like it does on UNIX, pure OCaml libraries
are
trivial to install, and the binaries don’t depend on cygwin.
Note
that “opam switch create” also just works, you can install
either
MinGW or MSVC compiler versions as opam switches. I only ever
start
the Windows VM to make release builds, and the workflow is
exactly the
same as on Linux where I’m actually writing code.
My only obstacle on that path was that FileUtils lost its
Windows
compatibility, but I wanted to use it, so I worked with
@gildor478 to
make it cross-platform again. Uncovered a bug in the
implementation of
Unix.utimes in the process, but it’s hardly a commonly used
function.
You can also setup AppVeyor builds. It’s not as simple as I wish
it
would be, but there are projects doing it that you can steal the
setup
from.
There’s also opam-cross-windows, but it’s very incomplete and
needs
work to be practical. There are no big obstacles, it just needs
work. While files in opam-repository-mingw are normally
identical to
the default opam repository, the cross one needs small
adjustments in
every package to specify the toolchain to use, so the required
work is
mostly a lot of trivial but manual actions. I hope eventually it
reaches parity with fdopen’s one and we’ll be able to easily
build for
Windows without ever touching Windows.
As of static Linux builds, @JohnWhitington’s approach can work,
but
there’s a better option if you don’t need anything from glibc
specifically and don’t link against any C libs: build statically
with
musl. There’s a `+musl+static+flambda' compiler flavour. You
need musl
and gcc-musl to install it, but after that, just build with
`-ccopt
-static' flag and you get a binary that doesn’t depend on
anything.
[soupault 4] <https://soupault.neocities.org/>
Dune 2.0.0
══════════
Archive: <https://discuss.ocaml.org/t/ann-dune-2-0-0/4758>
rgrinberg announced
───────────────────
On behalf of the dune team, I’m delighted to announce the
release of
dune 2.0. This release is the culmination of 4 months of hard
work by
the dune team and contains new features, bug fixes, and
performance
improvements . Here’s a selection of new features that I
personally
find interesting:
• New boostrap procedure that works in low memory environments
• (`deprecated_library_name' ..) stanza to properly deprecate
old
library names
• (`foreign_library' ..) stanza to define C/C++ libraries.
• C stubs directly in OCaml executables
Refer to the change log for an exhaustive list.
We strive for a good out of the box experience that requires no
configuration, so we’ve also tweaked a few defaults. In
particular, `$
dune build' will now build `@all' instead of `@install', and
ocamlformat rules are setup by default.
Lastly, dune 2.0 sheds all the legacy related to jbuilder and
will no
longer build jbuilder projects. This change is necessary to ease
maintenance and make it easier to add new features down the
line. There are a few other minor breaking changes. Refer to the
change log for the full list. We apologize in advance for any
convenience this might cause.
[Changelog]
[Changelog] <https://discuss.ocaml.org/t/ann-dune-2-0-0/4758>
Advanced C binding using ocaml-ctypes and dune
══════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/advanced-c-binding-using-ocaml-ctypes-and-dune/4805>
toots announced
───────────────
I worked on a socket.h binding last summer and had a great
experience
integrating ocaml-ctypes with dune, I thought that might be of
interest to other developers so I wrote about it:
<https://medium.com/@romain.beauxis/advanced-c-binding-using-ocaml-ctypes-and-dune-cc3f4cbab302>
rgrinberg replied
─────────────────
This is a good article. I encourage anyone who writes C bindings
with
ctypes to study it carefully.
A little bit of advice to shorten your dune files:
┌────
│ (deps (:gen ./gen_constants_c.exe))
└────
This line isn’t necessary. Dune is smart enough to know that
running a
binary in a rule incurs a dependency on it.
dune has a truly amazing [support for cross-compiling],
which we do not cover here, but, unfortunately, its
primitives for building and executing binaries do not yet
cover this use case.
Indeed, we don’t have any primitives for running binaries on the
target platform. Perhaps we should add some. However, we do in
fact
have some features in dune to solve this concrete cross
compilation
problem. As far as I understand, the goal is to obtain some
compile
time values such as #define constants and field offsets for the
target
platform. This does not in fact require to run anything on the
cross
compilation target. In configurator, we have a primitive
`C_define.import' to extract this information. The end result is
that
these configurator scripts are completely compatible with cross
compilation.
Perhaps this could be generalized to work with ctypes generators
as
well?
Funny bit of trivia: The hack in configurator required to do
this is
in fact something I extracted from ctypes itself. The original
author
is [whitequark], who in turn wrote it to make ctypes itself
amendable
to cross compilation.
[support for cross-compiling]
<https://dune.readthedocs.io/en/latest/cross-compilation.html>
[whitequark] <https://github.com/whitequark>
emillon then added
──────────────────
This does not in fact require to run anything on the cross
compilation target. In configurator, we have a primitive
`C_define.import' to extract this information. The end
result is that these configurator scripts are completely
compatible with cross compilation.
If anybody wants to know more about this bit, I wrote an article
about
this last year:
<https://dune.build/blog/configurator-constants/>
Upcoming breaking change in Base/Core v0.14
═══════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/upcoming-breaking-change-in-base-core-v0-14/4806>
bcc32 announced
───────────────
We’re changing functions in Base that used to use the
polymorphic
variant type `[ `Fst of 'a | `Snd of 'b ]' to use `('a, 'b)
Either.t'
instead. As well as enabling the use of all of the functions in
the
Either module, this makes the functions consistent with other
functions that already use `Either.t', (currently just
`Set.symmetric_diff')
The following functions’ types will change:
• `Result.ok_fst'
• `List.partition_map'
• `Map.partition_map', `Map.partition_mapi'
• `Hashtbl.partition_map', `Hashtbl.partition_mapi'
The type of List.partition3_map will not change:
┌────
│ val partition3_map
│ : 'a t
│ -> f:('a -> [ `Fst of 'b | `Snd of 'c | `Trd of 'd ])
│ -> 'b t * 'c t * 'd t
└────
We don’t have a generic ternary variant, and it doesn’t seem
worth it
to mint one just for this purpose.
Since this change is pretty straightforward, we expect that a
simple
find/replace will be sufficient to update any affected call
sites.
CI/CD Pipelines: Monad, Arrow or Dart?
══════════════════════════════════════
Archive:
<https://roscidus.com/blog/blog/2019/11/14/cicd-pipelines/>
Thomas Leonard announced
────────────────────────
In this post I describe three approaches to building a language
for
writing CI/CD pipelines. My first attempt used a monad, but this
prevented static analysis of the pipelines. I then tried using
an
arrow, but found the syntax very difficult to use. Finally, I
ended up
using a light-weight alternative to arrows that I will refer to
here
as a dart (I don’t know if this has a name already). This allows
for
static analysis like an arrow, but has a syntax even simpler
than a
monad.
<https://roscidus.com/blog/blog/2019/11/14/cicd-pipelines/>
Use of functors to approximate F# statically resolved type
parameters
═════════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/use-of-functors-to-approximate-f-statically-resolved-type-parameters/4782>
cmxa asked
──────────
I am learning OCaml coming from F#. In F#, to calculate the
average of
an array whose element type supports addition and division, one
can
write
┌────
│ let inline average (arr: 'a[]) : 'a
│ when ^a : (static member DivideByInt : ^a * int -> ^a)
│ and ^a : (static member (+) : ^a * ^a -> ^a)
│ and ^a : (static member Zero : ^a)
│ =
│ if Array.length arr = 0 then
(LanguagePrimitives.GenericZero) else
│ LanguagePrimitives.DivideByInt (Array.fold (+)
(LanguagePrimitives.GenericZero) arr) (Array.length arr)
└────
My understanding is that in OCaml, one would have a module type
like
so:
┌────
│ module type Averagable = sig
│ type 'a t
│
│ val divide_by_int : 'a -> int -> 'a
│ val plus : 'a -> 'a -> 'a
│ val zero : 'a
│ end
└────
My question is how the corresponding function would be written:
┌────
│ let average arr =
│ ???
└────
smolkaj replied
───────────────
First, `Averagable' should look like this:
┌────
│ module type Averagable = sig
│ type t
│ val divide_by_int : t -> int -> t
│ val plus : t -> t -> t
│ val zero : t
│ end
└────
Then average will look something like this:
┌────
│ let average (type t) (module A : Averagable with type t = t)
(arr : t array) : t =
│ Array.fold ~init:A.zero ~f:A.plus arr
└────
(The code above uses Jane Street’s Base/Core library.)
ivg then added
──────────────
While @smolkaj’s answer is a correct and direct implementation
of your
F# code, it might be nicer if your code can interplay with
existing
abstractions in the OCaml infrastructure. For example,
┌────
│ open Base
│
│ let average (type a) (module T : Floatable.S with type t = a)
xs =
│ Array.fold ~init:0. ~f:(fun s x -> s +. T.to_float x) xs /.
│ Float.of_int (Array.length xs)
└────
and now it could be used with any existing numeric data in
Base/Core
┌────
│ average (module Int) [|1;2;3;4|];;
│ - : Base.Float.t = 2.5
└────
and even adapted to non-numbers,
┌────
│ let average_length = average (module struct
│ include String
│ let to_float x = Float.of_int (String.length x)
│ let of_float _ = assert false
│ end)
└────
The latter example shows that we requested more interface than
need, a
cost that we have to pay for using an existing definition. In
cases
when it matters, you can specify the specific interface, e.g.,
┌────
│ module type Floatable = sig
│ type t
│ val to_float : t -> float
│ end
│
│ let average (type a) (module T : Floatable with type t = a) xs
=
│ Array.fold ~init:0. ~f:(fun s x -> s +. T.to_float x) xs /.
│ Float.of_int (Array.length xs)
└────
But we reached the point where using first class modules is
totally
unnecessary. Our interface has only one function, so the
following
definition of average, is much more natural
┌────
│ let average xs ~f =
│ Array.fold ~init:0. ~f:(fun s x -> s +. f x) xs /.
│ Float.of_int (Array.length xs)
└────
it has type `'a array -> f:('a -> float) -> float' and computes
an
average of `f x_i' for all elements in the array.
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
it to you, or go take a look at [the archive] or the [RSS feed
of the
archives].
If you also wish to receive it every week by mail, you may
subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives]
<http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-12-10 8:21 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-12-10 8:21 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 4145 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of December 03
to 10,
2019.
Table of Contents
─────────────────
Internships at Nomadic-labs
Interesting OCaml Articles
Next OUPS meetup December 18th 2019
Old CWN
Internships at Nomadic-labs
═══════════════════════════
Archive:
<https://discuss.ocaml.org/t/internship-at-nomadic-labs/4819>
Julien Tesson announced
───────────────────────
Nomadic Labs is currently looking for students with an interest
in
functional programming for internships that would take place in
our
offices in Paris or Grenoble.
We have a catalog of internships topics available at [1] The
internships topics are mainly addressed to master student but
other
well motivated application will be considered.
A first selection phase on received résumé will occur on
december
15th. Please contact us at contact@nomadic-labs.com by
specifying
which topics in the catalog you're interested in.
[1]: <https://nomadic-labs.com/download/internship_catalog.pdf>
Please, feel free to redistribute widely.
Interesting OCaml Articles
══════════════════════════
Archive:
<https://discuss.ocaml.org/t/interesting-ocaml-articles/1867/57>
james woodyatt announced
────────────────────────
Found on *Lobste.rs*: Mark Karpov writes yet another [Haskell
vs. OCaml] for old time's sake. I found it worth a read and a
mention
here.
p.s. He spends a bit of time in the intro lamenting the lack of
a
conventional Unicode string library for OCaml, and I feel that
pain
acutely, especially since I'm the author of an *unconventional*
one,
i.e. the [Ucs_text] module in my [Orsetto] project.
[Haskell vs. OCaml]
<https://markkarpov.com/post/haskell-vs-ocaml.html>
[Ucs_text]
<https://bitbucket.org/jhw/orsetto/src/default/src/ucs/ucs_text.mli>
[Orsetto] <https://bitbucket.org/jhw/orsetto>
Next OUPS meetup December 18th 2019
═══════════════════════════════════
Archive:
<https://sympa.inria.fr/sympa/arc/caml-list/2019-12/msg00009.html>
Bruno Bernardo announced
────────────────────────
The OUPS meetup is back. The next one will take place on
Wednesday,
December 18, 7pm at IRILL on the Jussieu campus. As usual, we
will
have a few talks, followed by pizzas and drinks.
The talks will be the following:
• Nathan Rebours, The future of OCaml-PPX
• Guillaume Claret, coq-of-ocaml
(<https://clarus.github.io/coq-of-ocaml/>)
And possibly a third talk. Contact us if you want to present
something, especially if you have a small project you want to
show in
10-15min.
To register, or for more information, go here:
<https://www.meetup.com/ocaml-paris/events/267019458>
*Registration is required! Access is not guaranteed after 7pm if
you're not registered.* (It also helps us to order the right
amount of
food.)
Access map:
IRILL - Université Pierre et Marie Curie (Paris VI)
Barre 15-16 1er étage
4 Place Jussieu
75005 Paris
<https://www.irill.org/pages/access.html>
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and
I'll mail
it to you, or go take a look at [the archive] or the [RSS feed
of the
archives].
If you also wish to receive it every week by mail, you may
subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives]
<http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-12-17 8:52 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-12-17 8:52 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1.1.1: Type: text/plain, Size: 6972 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of December 10 to 17,
2019.
Table of Contents
─────────────────
Is there a good way to encode linear types in OCaml?
Arch Linux installer written in OCaml
batteries batteries.2.11.0
Old CWN
Is there a good way to encode linear types in OCaml?
════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/is-there-a-good-way-to-encode-linear-types-in-ocaml/1292/7>
Continuing this old thread, Konstantin Olkhovskiy said
──────────────────────────────────────────────────────
I've stumbled upon a library that implements linear types for OCaml,
using monads, lens and some ppx to make it more lightweight. Might be
of interest: <https://github.com/keigoi/linocaml>
Anton Kochkov added
───────────────────
It is the part of even more interesting system - [OCaml MPST]
(Multiparty Session Types) See the [slides].
[OCaml MPST] <https://github.com/keigoi/ocaml-mpst>
[slides]
<https://www.slideshare.net/keigoi/ocamlmpst-global-protocol-combinators-175519214>
Guillaume Munch-Maccagnoni then said
────────────────────────────────────
(The paper linked on that page is dated 2011/2014. In case anyone
wonders whether the authors have found a time machine in a barn to be
able to cite papers from 2018, there just seems to be an error in the
preparation. It is freshly published, and a PDF with correct dates is
available [here].)
[here]
<https://www.jstage.jst.go.jp/article/ipsjjip/27/0/27_431/_article>
Arch Linux installer written in OCaml
═════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/arch-linux-installer-written-in-ocaml/4388/12>
Darren announced
────────────────
I'm doing a short update here as Oali has seen some significant
changes. This update is also the last one here to avoid being too
annoying, and also since I won't be add too much new stuff to Oali in
foreseeable future.
Major changes since last time
• SaltStack files and script files (or profiles) now live in a
separate [repo]
• Oali accepts custom profile repo URL to facilitate using your own
SaltStack files without forking Oali itself
• Semi self-documentation
• Added mechanism to facilitate inline documentation inside
`oali.ml' itself
• The generated markdown doc is stored as [OALI_DOC] in repo, it
lists all the steps (or tasks) Oali does, along with descriptions
• Added LVM support
• Works with all 3 disk layouts, and encryption
• See [here] for details on added logical volumes
• Answer remembering of dialogues when appropriate
• Relatively static answers (e.g. hostname, whether to use
encryption, LVM) are stored in `oali_answers' directory, with a
JSON file for each task
• The "answer store" can be used in new session of Oali. The old
answer store is wiped accordingly if user changes their answer.
• Added SSH server setup and public key transfer code (ported from old
server bash script)
• See [here] for details
• Mainly useful for when you have (virtual) console access to live
CD/Oali install screen, and want to add needed public key to the
user's `.ssh/authorized_keys' via network instead of loading from
physical medium
I've used Oali to install in various configurations in past couple of
days, and have yet to notice major defects. That being said, exercise
caution as you would for installing an OS.
[repo] <https://github.com/darrenldl/oali-profiles>
[OALI_DOC] <https://github.com/darrenldl/oali/blob/master/OALI_DOC.md>
[here]
<https://github.com/darrenldl/oali/blob/master/OALI_DOC.md#20-set-up-disk>
[here]
<https://github.com/darrenldl/oali/blob/master/OALI_DOC.md#54-transfer-ssh-public-keys>
batteries batteries.2.11.0
══════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-batteries-batteries-2-11-0/4871/1>
UnixJunkie announced
────────────────────
The latest 2.x release of batteries is available in opam. OCaml
batteries included is a community maintained extended standard
library.
<https://github.com/ocaml-batteries-team/batteries-included>
The API documentation is hosted here:
<https://ocaml-batteries-team.github.io/batteries-included/hdoc2/>
Here is the changelog:
┌────
│ v2.11.0 (minor release)
│
│ This minor release fixes a few bugs or interface mismatch with OCaml stdlib,
│ and is compatible with BER MetaOCaml.
│
│ This is the last planned release of the v2 series.
│ Next planned release (v3.0.0) will introduce some API changes.
│
│ Notable changes:
│
│ Add Unix.with_locked_file
│ #904
│ (Simon Cruanes, Cedric Cellier, review by Francois Berenger)
│
│ Build with -strict-sequence
│ #927
│ (Armaël Guéneau, review by Francois Berenger)
│
│ Add Legacy.Result for OCaml >= 4.8.0
│ #913
│ (Cedric Cellier, review by Francois Berenger)
│
│ Remove BatOo
│ #915
│ (Cedric Cellier, review by Francois Berenger)
│
│ Add BatFilename
│ #910
│ (Cedric Cellier, review by Francois Berenger)
│
│ Make batteries usable with BER MetaOCaml
│ #909
│ (Cedric Cellier, review by Francois Berenger and Gabriel Scherer)
│
│ Unix.sleepf is provided across all OCaml versions;
│ previously it was only for OCaml >= 4.03.0
│ #930
│ (Francois Berenger, review by Cedric Cellier)
└────
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and I'll mail
it to you, or go take a look at [the archive] or the [RSS feed of the
archives].
If you also wish to receive it every week by mail, you may subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives] <http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2019-12-31 9:18 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2019-12-31 9:18 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1: Type: text/plain, Size: 14554 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of December 17 to 31,
2019.
Sorry for the hiatus last week, I was away with no internet
access. Happy new year!
Table of Contents
─────────────────
Internships at Be Sport (OCaml, Ocsigen)
ocaml-lsp preview
Reproducible builds with OCaml / opam and MirageOS
the OCaml Software Foundation
soupault: a static website generator based on HTML rewriting
Release of owl-symbolic 0.1.0
Old CWN
Internships at Be Sport (OCaml, Ocsigen)
════════════════════════════════════════
Archive:
<https://sympa.inria.fr/sympa/arc/caml-list/2019-12/msg00023.html>
Be Sport announced
──────────────────
Be Sport currently has several open internship positions for OCaml
developers.
Keywords: OCaml, Ocsigen, Mobile app development, Web, Database,
Sport, Social networks
Be Sport develops the first global platform dedicated to sport, in
collaboration with prominent actors of sport in France and in the
world. All our development is done in OCaml. Our Web and mobile apps
(iOS, Android) are developed as a multi-tier app using the Ocsigen
framework. Our premises are located in the center of Paris.
Please contact me for more information.
ocaml-lsp preview
═════════════════
Archive: <https://discuss.ocaml.org/t/ann-ocaml-lsp-preview/4876/1>
Rudi Grinberg announced
───────────────────────
I'm excited to announce [ocaml-lsp]. This project contains an
implementation of an LSP server for the OCaml language. The current
implementation piggy backs on the widely successful [merlin] tool to
provide completion & type inference. In the future, we'd like to use
all other essential tools such as ocamlformat, odoc, dune to provide
more functionality in your editors.
For now, the project isn't yet available on opam as we're still
polishing some rough edges in the release process. Nevertheless, I
invite all brave souls who are ready to experiment to give this lsp
server a try. Your feedback & contributions are most welcome
:slight_smile:
[ocaml-lsp] <https://github.com/ocaml/ocaml-lsp>
[merlin] <https://github.com/ocaml/merlin>
UnixJunkie asked and Anton Kochkov replied
──────────────────────────────────────────
This project looks nice.
If I am an Emacs or Vi user, can I take advantage of an
LSP server?
Or, is this only for some new editors like Atom or VScode?
@UnixJunkie of course! That's the whole point of this tooling.
For Vim you can choose between:
• [Coc.nvim] - most powerful of all, but written in TypeScript and
heaviest of all
• [Ale] - pure VimL
• [vim-lsp] - pure VimL
• [LanguageClient-neovim] - written in Rust
• Some other implementations
I am not an Emacs expert, but there is amazing LSP integration too:
• [lsp-mode]
<https://aws1.discourse-cdn.com/standard11/uploads/ocaml/original/2X/b/b8acd745527e801fef1eb3d4e8722d49c5c2ed1a.png>
[Coc.nvim] <https://github.com/neoclide/coc.nvim>
[Ale] <https://github.com/dense-analysis/ale>
[vim-lsp] <https://github.com/prabirshrestha/vim-lsp>
[LanguageClient-neovim]
<https://github.com/autozimu/LanguageClient-neovim>
[lsp-mode] <https://github.com/emacs-lsp/lsp-mode>
Pau Ruiz Safont said
────────────────────
Neovim 0.5.0 (now pre-released) has native LSP support as well:
<https://github.com/neovim/neovim/pull/11336>
Not sure how well integrated is it going to be with various plugins
([example])
[example] <https://github.com/Shougo/deoplete-lsp>
Anton Kochkov added
───────────────────
NeoVim 0.5.0 will also include the [tree-sitter] parser for syntax
highlighting, which will allow way better coloring. And tree-sitter
already has [OCaml grammar], so implementing semantics-aware syntax
highlighter will be easier. But I expect the support more or less
ready for external contributions only in 0.6.0, sadly. Integrating the
tool with something like [GitHub Semantic] (*Haskell alert*) will
greatly improve OCaml experience on GitHub too, see the [corresponding
issue].
[tree-sitter] <https://tree-sitter.github.io/tree-sitter/>
[OCaml grammar] <https://github.com/tree-sitter/tree-sitter-ocaml>
[GitHub Semantic] <https://github.com/github/semantic>
[corresponding issue] <https://github.com/github/semantic/issues/138>
Pieter Goetschalckx said
────────────────────────
The next step for Semantic support is documented [here], but I'm
working on some [improvements] of the tree-sitter parser first.
[here]
<https://github.com/tree-sitter/haskell-tree-sitter/blob/master/docs/codegen.md>
[improvements]
<https://github.com/tree-sitter/tree-sitter-ocaml/pull/36>
Carlos D'Agostino said
──────────────────────
For Emacs there is also `eglot': <https://github.com/joaotavora/eglot>
– As the README says, it's quite minimalist compared to `lsp-mode'.
Reproducible builds with OCaml / opam and MirageOS
══════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/reproducible-builds-with-ocaml-opam-and-mirageos/4877/1>
Hannes Mehnert announced
────────────────────────
I wrote up recent developments about reproducible builds with opam –
including some tooling <https://hannes.nqsb.io/Posts/ReproducibleOPAM>
Thanks to everyone involved in the effort to get OCaml and opam
deterministic
• Nov 2015 [I collected downstream patches and asked kindly to get
them upstream] (temporary flle names in binaries, timestamps)
• Dec 2017 [BUILD_PATH_PREFIX_MAP support] (and further patches for
that)
• Dec 2018 Paris summit [opam reproducibility] [MirageOS]
• [`orb'] tool for reproducibility testing (so much better than the
shell scripts I used in the meantime)
• Dec 2019 [Marrakesh summit]
The journey is not yet finished, we're in a pretty good shape, but
further testing and tooling is needed to expose the information "is my
library reproducible?" to OCaml developers.
I'm interested in feedback, please let us discuss this further here in
case you're interested. :D
[I collected downstream patches and asked kindly to get them upstream]
<https://github.com/ocaml/ocaml/issues/7037>
[BUILD_PATH_PREFIX_MAP support]
<https://github.com/ocaml/ocaml/pull/1515>
[opam reproducibility]
<https://reproducible-builds.org/events/paris2018/report/#Toc11410_331763073>
[MirageOS]
<https://reproducible-builds.org/events/paris2018/report/#Toc11681_331763073>
[`orb'] <https://github.com/rjbou/orb>
[Marrakesh summit]
<https://reproducible-builds.org/events/Marrakesh2019/>
Anil Madhavapeddy added
───────────────────────
An absolutely amazing cross-layer effort; well done on pushing all
this through @hannes! I really enjoyed reading the minutes of the
Paris summit last year:
<https://reproducible-builds.org/events/paris2018/report/#Toc11681_331763073>
the OCaml Software Foundation
═════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-the-ocaml-software-foundation/4476/13>
Continuing this thread, gasche announced
────────────────────────────────────────
A small report on the actions that we launched since my initial
posting.
(There was also some progress on the "enabling individual donations"
front, maybe something will be possible in the next few months. Don't
start holding your breath yet.)
• We are funding the "Leafs" research project in Lisbon to develop
teaching material for theoretical-computer-science courses (automata
and stuff) in OCaml, with interactive visualization components, some
of which will hopefully be integrated in the [Learn-OCaml] platform
over the course of 2020/2021.
• We provide funding for the [Gallium/Cambium] research team at INRIA
Paris (France), an active place for OCaml-related fundamental
research (some of the team members are also very active on the
implementation front, for example Xavier Leroy, Damien Doligez,
Florian @octachron Angeletti, and Sébastien Hinderer).
• We sponsor the [SWERC] programming contest for 2019-2020, and in
return the contest added OCaml to the list of available
languages. Most participants to these competitive-programming events
use C++, but we talked to past and active participants who said they
would be interested in using OCaml on some problems with more
symbolic computation.
• Over the course of the 4.10 release process, we are funding work by
@kit-ty-kate to have a wide look at the ecosystem and improve
compatibility with the upcoming release. (I believe that the
upstream PR [#9176] is a first result of this effort.)
• In reaction to the Discourse thread [Suggestions for OCaml
documentation], we are planning to fund further work by @sanette to
experiment with the HTML rendering of the OCaml manual, in
coordination with @octachron to try to upstream improvements when
reasonably possible.
• We got in touch with the [Owl] project to sponsor a development
sprint in 2020.
[Learn-OCaml] <http://ocaml-sf.org/learn-ocaml.html>
[Gallium/Cambium] <http://cambium.inria.fr/>
[SWERC] <https://swerc.eu/2019/about/>
[#9176] <https://github.com/ocaml/ocaml/pull/9176>
[Suggestions for OCaml documentation]
<https://discuss.ocaml.org/t/suggestions-for-ocaml-documentation/4504>
[Owl]
<https://discuss.ocaml.org/t/suggestions-for-ocaml-documentation/4504>
soupault: a static website generator based on HTML rewriting
════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-soupault-a-static-website-generator-based-on-html-rewriting/4126/10>
Daniil Baturin announced
────────────────────────
Made a [1.7.0 release].
First improvement is that you now can pipe the content of any element
through any external program with `preprocess_element' widget (PR by
Martin Karlsson). For example, insert inline SVG versions of all
graphviz graphs from `<pre class="language-graphviz">' and also
highlight the Dot source itself with [highlight] (or any other tool of
your choice):
┌────
│ [widgets.graphviz-svg]
│ widget = 'preprocess_element'
│ selector = 'pre.language-graphviz'
│ command = 'dot -Tsvg'
│ action = 'insert_after'
│
│ [widgets.highlight]
│ after = "graphviz-svg"
│ widget = "preprocess_element"
│ selector = '*[class^="language-"]'
│ command = 'highlight -O html -f --syntax=$(echo $ATTR_CLASS | sed -e "s/language-//")'
│ action = "replace_content" # default
└────
<https://aws1.discourse-cdn.com/standard11/uploads/ocaml/original/2X/a/a4d8cc05d65634de0faf3c05b16e0de8d27a78a3.png>
Two other improvements are multiple index "views" and default value
option for custom index fields, like
┌────
│ [index.custom_fields]
│ category = { selector = "span#category", default = "Misc" }
└────
[1.7.0 release]
<https://soupault.neocities.org/blog/soupault-1.7.0-release>
[highlight] <http://andre-simon.de>
Release of owl-symbolic 0.1.0
═════════════════════════════
Archive:
<https://discuss.ocaml.org/t/announce-release-of-owl-symbolic-0-1-0/4930/1>
jrzhao42 announced
──────────────────
We are please to release [owl-symbolic 0.1.0]. It fully supports
defining a computation graph and running on accelerators (TPU/GPU) via
[ONNX] specification. It also aims to support converting an Owl
computation graph into symbolic representation and then to ONNX
model. The module also has some cool features like converting a
computation graph into LaTeX string, and then showing the result in a
web UI, etc.
We implements a full neural network module atop of it (the interface
of which is basically identical to that in Owl's core). It turns out
that the design of `owl-symbolic' is so nice that the DNN module only
has 179 LOC! You can easily define popular DNN architectures such as
Inception, ResNet, VGG, etc. just like in Owl.
This is still an on-going project and a lot remains to be
done. Despite its name, `owl-symbolic' does not do any useful computer
algebra (CAS) stuff at the moment, but CAS is indeed on our TODO.
For more information, please check out the related section in [Owl
tutorial book].
[owl-symbolic 0.1.0] <https://opam.ocaml.org/packages/owl-symbolic/>
[ONNX] <https://onnx.ai/>
[Owl tutorial book] <https://ocaml.xyz/owl_tutorials/symbolic.html>
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and I'll mail
it to you, or go take a look at [the archive] or the [RSS feed of the
archives].
If you also wish to receive it every week by mail, you may subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives] <http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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^ permalink raw reply [flat|nested] 12+ messages in thread
* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2020-01-07 13:43 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2020-01-07 13:43 UTC (permalink / raw)
To: lwn, cwn, caml-list
[-- Attachment #1: Type: text/plain, Size: 23631 bytes --]
Hello
Here is the latest OCaml Weekly News, for the week of December 31, 2019
to January 07, 2020.
Table of Contents
─────────────────
ocaml-lsp preview
Mkocaml Release - Project generator
Garbage Collection, Side-effects and Purity
A Lightweight OCaml Webapp Tutorial (Using Opium, Caqti, and Tyxml)
Release of owl-symbolic 0.1.0
Static lifetime
Old CWN
ocaml-lsp preview
═════════════════
Archive: <https://discuss.ocaml.org/t/ann-ocaml-lsp-preview/4876/15>
Continuing this thread, Edwin Török said
────────────────────────────────────────
Here is an example with ALE and Neovim (tested with v0.3.8):
• Install the [Ale] plugin. If your Vim has support for packages (Vim
8+ or Neovim) you can simply clone it in the correct subdir, no need
for a plugin manager: `git clone https://github.com/w0rp/ale.git
.vim/pack/my-plugins/start/ale'
• Add this to your .vimrc:
┌────
│ " only invoke merlin to check for errors when
│ " exiting insert mode, not on each keystroke.
│ let g:ale_lint_on_text_changed="never"
│ let g:ale_lint_on_insert_leave=1
│
│ " enable ALE's internal completion if deoplete is not used
│ let g:ale_completion_enabled=1
│
│ " only pop up completion when stopped typing for ~0.5s,
│ " to avoid distracting when completion is not needed
│ let g:ale_completion_delay=500
│
│ " see ale-completion-completeopt-bug
│ set completeopt=menu,menuone,preview,noselect,noinsert
│
│ if has('packages')
│ packloadall
│
│ " This should be part of ALE itself, like ols.vim
│ call ale#linter#Define('ocaml',{
│ \ 'name':'ocaml-lsp',
│ \ 'lsp': 'stdio',
│ \ 'executable': 'ocamllsp',
│ \ 'command': '%e',
│ \ 'project_root': function('ale#handlers#ols#GetProjectRoot')
│ \})
│
│ " remap 'gd' like Merlin would
│ nmap <silent><buffer> gd <Plug>(ale_go_to_definition_in_split)<CR>
│
│ " go back
│ nnoremap <silent> <LocalLeader>gb <C-O>
│
│ " show list of file:line:col of references for symbol under cursor
│ nmap <silent><buffer> <LocalLeader>go :ALEFindReferences -relative<CR>
│
│ " Show documentation if available, and type
│ nmap <silent><buffer> <LocalLeader>hh <Plug>(ale_hover)<CR>
│
│ " So I can type ,hh. More convenient than \hh.
│ nmap , <LocalLeader>
│ vmap , <LocalLeader>
│ endif
└────
[Ale] <https://github.com/dense-analysis/ale>
Mkocaml Release - Project generator
═══════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/mkocaml-release-project-generator/4949/1>
Chris Nevers announced
──────────────────────
I recently created a tool to generate OCaml projects. I constantly
have difficulties with dune commands and setting up opam files,
etc. Mkocaml generates a dune project with inline tests, opam file,
git repository, git ignore, and a Makefile with easy commands. This
tool can be of great help to newcomers, allowing them to get up and
running faster!
<https://github.com/chrisnevers/mkocaml>
Garbage Collection, Side-effects and Purity
═══════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/garbage-collection-side-effects-and-purity/4737/1>
Gerard asked
────────────
GC = Garbage Collection
GC, in a pure program, is a point that's always confused me. I always
understood that freeing memory from a program was impure and would
create side-effects but it seems it doesn't matter if the program is
remove from all consequences of those impure acts and side-effects.
Basically, if any memory block has no remaining references in the
program, then freeing that block will have no consequences on the
running program so its allowed to happen behind the scenes..
Is this correct reasoning?
Guillaume Munch-Maccagnoni replied
──────────────────────────────────
To answer your question “does de-allocation creates a side-effect?”:
To state the obvious: if you care about the memory consumption of your
program, then you care about the side-effect of de-allocation, and
this indeed voids purity.
A language like OCaml lets you reason about de-allocation. Memory is
collected when values are no longer reachable. Like in other
languages, 1) a value that does not escape and goes out of scope will
get collected, and 2) you can reason about when a value escapes and
goes out of scope thanks to OCaml respecting the strict evaluation
order of value types. OCaml (like other compiled languages) is in fact
more precise: it ties the dynamic notion of reachability to the
lexical notion of variable occurrence. For instance, in the following:
┌────
│ let x = get_huge_data () in
│ let z = long_running_function x in
│ f z
└────
OCaml will be able to collect the value in `x' before `x' goes out of
scope, and thus if possible before `long_running_function'
returns. Indeed, OCaml performs liveness analysis during compilation,
and records the information about variable occurrences in frame
descriptors, for consumption by the GC when it scans for roots. In
fact, you can rely on call-by-value operational semantics to (loosely)
reason that a value no longer appears in a program, and therefore that
the corresponding memory will be collected by the GC¹ ([Morrisett,
Felleisen and Harper, "Abstract Models of Memory Management"]). Of
course, using lazy or higher-order interfaces (when closures escape;
with many idioms they do not) will make it harder to reason about the
lifetime of values.
(¹: For OCaml, this is a conjecture I make, for subsets which could be
given such operational semantics, and only for native
compilation. Morrisett, Felleisen and Harper's semantics obviously
assumes that the results of liveness analysis are made available to
the GC, but this is not written, nor is there any mention of the link
between liveness analysis and accuracy of garbage collection in
Appel's "Modern Compiler Implementation in C". I assume that it was
part of folklore at the time, though recently I mentioned it to some
functional PL researcher and they seemed surprised. I only found it
explicitly mentioned in later papers from the OOP community. I checked
that everything seems in place for OCaml to allow such reasoning, but
only the authors of the original code, @xavierleroy and
@damiendoligez, can tell us if this is intended to be part of the
language semantics.)
Furthermore, memory is not collected immediately when a value becomes
unreachable. Instead:
• Short-lived values are allocated contiguously and deallocated in a
batch, so that allocating and deallocating short-lived values is
very cheap, with additional benefits in terms of cache
locality. This replaces stack allocation from languages with
explicit memory management.
• Longer-lived values are moved to a heap that is scanned
incrementally, to ensure a bounded latency. In contrast, naive
reference-counting and unique pointers from C++/Rust make you pay
the cost of deallocation up-front.
While this is essential for understanding the performance of OCaml
programs, from the point of view of deallocation-as-an-effect, the
delaying of the collection of unreachable memory can be seen as a
runtime optimisation, that does not change the effectful status of
deallocation (the memory still gets freed). [The intuition is that an
effect can support some degree of reordering without requiring purity,
as illustrated by strong monads which can be commutative without being
idempotent, one possible definition of purity for semanticists.]
But is de-allocation an effect _in practice_? Faced with the
scepticism and misunderstandings from this thread, I emit two
hypotheses:
1) Memory consumption is not an issue in functional programming, for
application areas that interest functional programmers.
2) Memory management in OCaml is efficient in such a way that
programmers do not need to think about it in their day-to-day
programming activities in those terms.
Hypothesis 2) could be explained for instance if OCaml programmers are
already dealing with effects and thinking about the order in which
their code executes (my experience), and are only used to deal with
deallocation as an afterthought, e.g. when chasing leaks with a
profiler.
Let us turn towards two programming language experiments from the
1990's that allow me to reject hypothesis 1). Both show what happens
when one denies the status of deallocation as an effect controlled by
the programmer.
• Region-based memory management consisted in allocating in a stack of
memory _regions_ deallocated at once, and determined by a
whole-program static analysis. Now regarded as a failed idea but
successful experiment (i.e. good science!), it taught us a lot about
the structure of functional programs in relationship to memory
management ([see this retrospective]). There were some good
performance results, but also pathological cases _“where lifetimes
were not nested or where higher-order functions were used
extensively”_, sometimes requiring them to be altered to be _“region
friendly”_, which was _“time-consuming”_ and required knowledge of
the inference algorithm. In addition, the regions changed
unpredictably when the programs evolved, and memory leaks appeared
when the compiler inferred too wide regions.
• Haskell was (at the time) an experiment with lazy functional
programming. Pervasive laziness prevents reasoning about the
lifetime of values, and purity is a central assumption used by the
compiler for program transformations, which is antithetical with
reasoning about deallocation as an effect. It is well-known that
naive Haskell code has issues with memory leaks, and that realistic
Haskell programs have to follow "best practices" to avoid leaks, by
making extensive use of strictness annotations (e.g. bang
patterns). Unfortunately, I found it hard to find reliable academic
sources about lessons drawn from the experiment like the RBMM
retrospective. The best I could find on the topic of memory leaks is
the following blog post:
<https://queue.acm.org/detail.cfm?id=2538488>, from a Haskell
programmer who wrote in another post (linked from that one) _“My
suspicion is that many (most?) large Haskell programs have space
leaks, but they often go unnoticed”_. This is consistent with
comments I received from people with Haskell experience (first-hand,
one academic and one industrial) and about an industrial Haskell
consultant (second-hand) who reportedly commented that their main
job was to fix memory leaks (but maybe in jest). Of course, take
this with a grain of salt. At least, I believe that the Haskell
academic community has accumulated empirical evidence of the extent
and manner in which deallocation voids purity assumptions. Having an
authoritative source about it would be pretty important to me, given
the initial promises of functional programs being more tractable
mathematically specifically via “referential transparency” and
independence of execution order, whose theoretical justification
already looks shaky to me from a semantic point of view. Some parts
of the literature continues to promise far-reaching consequences of
equational reasoning, without clear statements of limitation of the
application domain. I have the impression that the Haskell which is
practiced in the real world is very different from what you can read
in some academic papers.
The hypothesis that deallocation matters as an effect, and that ML
makes it easy to program and reason about effects, seems to me a
strong argument explaining OCaml's predictable and competitive
performance.
So, thank you for your healthy scepticism.
[Morrisett, Felleisen and Harper, "Abstract Models of Memory
Management"] <https://dash.harvard.edu/handle/1/3293156>
[see this retrospective]
<https://link.springer.com/article/10.1023/B:LISP.0000029446.78563.a4>
Xavier Leroy replied
────────────────────
Concerning the "don't scan local variables that are dead" trick:
• Technically it is not "intended to be part of the language
semantics" because the bytecode compiler (ocamlc) doesn't implement
it, only the native-code compiler (ocamlopt).
• As far as I remember, I reinvented this trick circa 1993, but it
seems it was used earlier in the Lazy ML compiler by Augustsson and
Johnsson. See Appel and Shao's paper "An Empirical and Analytic
Study of Stack vs. Heap Cost for Languages with Closures", JFP,
1996, end of section 5.
Guillaume Munch-Maccagnoni the asked
────────────────────────────────────
TL;DR: the paper mentioned by @xavierleroy provides additional
references regarding the importance of liveness analysis for GC,
including a demonstration by Appel that this actually matters for
space complexity (thanks!). I find that a link is still missing with
an abstract semantics à la Morrisett, Felleisen & Harper. This seems
important to me because more theoretical works about time & space
complexity in the lambda-calculus seem to take for granted that
garbage collection implements something like the latter (i.e., how
does one specify and certify that a compiler is sound for space
complexity?).
Xavier Leroy replied
────────────────────
See for example [Closure Conversion is Safe for Space], by Zoe
Paraskevopoulou and Andrew W. Appel, ICFP 2019.
[Closure Conversion is Safe for Space]
<https://www.cs.princeton.edu/~appel/papers/safe-closure.pdf>
A Lightweight OCaml Webapp Tutorial (Using Opium, Caqti, and Tyxml)
═══════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/a-lightweight-ocaml-webapp-tutorial-using-opium-caqti-and-tyxml/4967/1>
Shon announced
──────────────
The tutorial is [hosted on gitlab pages], out of [this repository].
I put this together in response to some requests for introductory
material on the topic (here and on [/r/ocaml]. I don't have much
expertise to offer in this area, but I had hacked together some simple
servers based on Opium in the past few months, so it seemed like I
should be able to memorialize some of what I learned for the benefit
of others. I received some critical guidance by the Opium maintainers,
rgrinberg and anuragsoni, and from other resources online (mentioned
at the end of the tutorial).
Any feedback or improvements are welcome: this is my first time
writing such lengthy instructional material, and I'm sure there's lots
of room to make it better.
[hosted on gitlab pages] <https://shonfeder.gitlab.io/ocaml_webapp/>
[this repository] <https://gitlab.com/anuragsoni/ocaml_webapp>
[/r/ocaml] <https://www.reddit.com/r/ocaml/>
Release of owl-symbolic 0.1.0
═════════════════════════════
Archive:
<https://discuss.ocaml.org/t/announce-release-of-owl-symbolic-0-1-0/4930/2>
jrzhao42 announced
──────────────────
The Owl tutorial book URL address is now changed to:
<https://ocaml.xyz/book/symbolic.html>.
Static lifetime
═══════════════
Archive: <https://discuss.ocaml.org/t/static-lifetime/4908/19>
André asked and Guillaume Munch-Maccagnoni replied
──────────────────────────────────────────────────
> Is it possible to “statically” allocate a value? By this I mean mark
a value such that it gets ignored by the GC and lives until the
program exits?
This is indeed the purpose of Ancient, which comes with limitations
and does not allow you to reclaim the memory until you exit the
program. (I am curious to know how well it works with recent OCaml
versions.)
> it would be really interesting to learn whether Ocaml forbids blocks
outside the heap.
The OCaml runtime has two modes (chosen at compilation) for dealing
with so-called "out-of-heap" pointers. In the legacy one that Chet
remembers, the GC uses a page table when scanning to be able to tell
which pointers it possesses. In the "no-naked-pointers" mode devised
more recently for efficiency reasons, the page table is replaced by
looking at the colour in the header of the dereferenced
value. Out-of-heap values must be preceded by a header with colour
black. The no-naked-pointer mode is more restricted, because once a
static value is referenced, it can no longer be deallocated, as you
never know whether it is still reachable by the GC. This should be
enough to support Ancient.
> One should verify such intuitions experimentally, before trying to
fix them, but I’m not familiar with what OCaml profilers can do…
Excluding large long-lived data from the GC is an old idea. Among
recent developments, Nguyen et al. [1] distinguish a "control path"
(where the generational hypothesis is assumed to hold) from a "data
path" (where values are assumed to follow an "epochal" behaviour
(long-lived, similar lifetimes, benefit from locality), and are
excluded from GC). They give as motivation so-called "big data" and as
figures of pathological GC usage up to 50% of total runtime. I
remember reading similar figures from blog posts about large data sets
in OCaml. In reality this indeed depends on knobs you can turn on your
GC that can result in increased peak memory usage among
others. (Assuming infinite available memory, it is even possible to
let the GC share drop to 0%.)
@ppedrot reported to me that in a recent experiment with Coq, using an
Ancient-like trick to exclude some large, long-lived and
rarely-accessed values from being scanned (namely serialising them
into bigarrays), they saw an 8% performance improvement across the
board in benchmarks.
Multicore, if I understood correctly, aims to support only the
no-naked-pointer mode, and I am not sure what the page table will
become. Coq currently does some out-of-heap allocation in the VM, and
has been adapted to be compatible with the no-naked-pointer mode by
wrapping out-of-heap pointers into custom blocks. For scanning its
custom stack (which mixes in-heap and out-of-heap values), Coq sets up
a custom root-scanning function (`caml_scan_roots_hook`), which still
relies on the page table.
Note that having to wrap out-of-heap pointers in custom blocks is
(much!) less expressive: for instance with Ancient you can call
`List.filter` on a statically-allocated list (and correctly get a
GC-allocated list of statically-allocated values). With custom blocks
you cannot mix in-heap and out-of-heap values in this way.
For a type system to deal with "statically" allocated values, have a
look at Rust, which: 1) prevents cycles of reference-counting schemes
thanks to uniqueness, 2) can treat GC roots as resources to deal with
backpointers at the leaves of the value (cf. the interoperability with
SpiderMonkey's GC in Servo). A point of view that I like is that
tracing GCs and static allocation differ fundamentally by how they
traverse values for collection: traversing live values for the first
one, and traversing values at the moment of their death for the
other. This gives them distinct advantages and drawbacks so one can
see them as complementary. (See notably [2,3].) Static allocation is
interesting for performance in some aspects (no tracing, no read-write
barrier, reusability of memory cells, avoids calling the GC at
inappropriate times), but I find it even more interesting for
interoperability (e.g. exchanging values freely with C or Rust, or
[applications from that other thread]). It is natural to want to mix
them in a language.
As far as I understand, developing the runtime capabilities for OCaml
to deal with out-of-heap pointers without resorting to an expensive
page table is an engineering problem, not a fundamental one. If anyone
is interested in this, please contact me.
[1] Nguyen et al., [Yak : A High-Performance Big-Data-Friendly Garbage
Collector], 2016
[2] Bacon, Cheng and Rajan, [A Unified Theory of Garbage Collection],
2004
[3] Shahriyar, Blackburn and Frampton, [Down for the Count? Getting
Reference Counting Back in the Ring], 2012
[applications from that other thread]
<https://discuss.ocaml.org/t/using-a-bigarray-as-a-shared-memory-for-parallel-programming/4841/19>
[Yak : A High-Performance Big-Data-Friendly Garbage Collector]
<https://www.usenix.org/system/files/conference/osdi16/osdi16-nguyen.pdf>
[A Unified Theory of Garbage Collection]
<http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.439.1202&rep=rep1&type=pdf>
[Down for the Count? Getting Reference Counting Back in the Ring]
<https://dl.acm.org/citation.cfm?doid=2258996.2259008>
UnixJunkie also replied
───────────────────────
If you can store your long-leaved data into a bigarray, I think you
would reach the effect that you were looking for (no more GC scanning
of this data).
This was once advised to me by Oleg, for some performance-critical
section of some code.
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and I'll mail
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[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2020-01-14 14:17 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2020-01-14 14:17 UTC (permalink / raw)
To: lwn, cwn, caml-list
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Hello
Here is the latest OCaml Weekly News, for the week of January 07 to 14,
2020.
Table of Contents
─────────────────
Calling a single function on every member of a GADT?
OCamlPro's opam cheat sheet, with a new theme!
OCaml 4.10.0, first beta
Data engineer positions at Elastic, US/Canada/Western Europe (proximate to NA timezones)
Release of naboris 0.1.0 a simple http server
esy@0.6.0 release
Old CWN
Calling a single function on every member of a GADT?
════════════════════════════════════════════════════
Archive:
<https://sympa.inria.fr/sympa/arc/caml-list/2020-01/msg00007.html>
Ivan Gotovchits asked
─────────────────────
I'm basically trying to do the equivalent of this simple `fold'
function:
┌────
│ module Simple =
│ struct
│ type term =
│ | Int of int
│ | Add
│ | App of term * term
│
│ let rec fold i f = function
│ | Int _ as t -> f i t
│ | Add -> f i Add
│ | App (x, y) as t -> f (fold (fold i f x) f y) t
│ end
└────
… but using a GADT:
┌────
│ module Gadt =
│ struct
│ type _ term =
│ | Int : int -> int term
│ | Add : (int -> int -> int) term
│ | App : ('b -> 'a) term * 'b term -> 'a term
│
│ let rec fold : type a. 'r -> ('r -> _ term -> 'r) -> 'r = fun i f -> function
│ | Int _ as t -> f i t
│ | Add -> f i Add
│ (*
│ ^ Error: This pattern matches values of type (int -> int -> int) term
│ but a pattern was expected which matches values of type int term
│ Type int -> int -> int is not compatible with type int
│ *)
│ | App (x, y) as t -> f (fold (fold i f x) f y) t
│ end
└────
I've tried other variants of the syntax and got many encouragements
but no green flag from the type-checker. Why is the compiler
expecting an int term in there? I though the whole point of the `type
a. ...' syntax was to allow the matched type to vary from one pattern
to the next? Is there a way to do this?
Ivan Gotovchits replied
───────────────────────
It is the limitation of the let-bound polymorphism. A parameter of a
function is monomorphic in its body. The classical example doesn't
even reference any GADT,
┌────
│ let example f = f "hello", f 42
└────
It won't compile even though we can provide a polymorphic function
that can applied both to integers and to strings, e.g., `exampe (fun x
-> x)' should be possible, but not, because of the let-bounded
polymorphism. There are a few solutions available in OCaml, the
simplest is to use records, e.g.,
┌────
│ type app = {apply : 'a. 'a -> 'a}
│
│ let example {apply} = apply "hello", apply 42;;
│
│ val example : app -> string * int = <fun>
└────
Now we have `app' that is polymorphic. In your case, I would define a
visitor type, e.g.,
┌────
│ type 'r visitor = {visit : 'a. 'a term -> 'r -> 'r}
│
│ let rec fold : type a. 'r -> 'r visitor -> a term -> 'r =
│ fun i f t -> match t with
│ | Int _ as t -> f.visit i t
│ | Add as t -> f.visit i t
│ | App (x,y) as t ->
│ let i = fold i f x in
│ let i = fold i f y in
│ f.visit i t
└────
Jacques Garrigue also replied
─────────────────────────────
Actually, this is a rare case where using a polymorphic method may be
handy too:
┌────
│ let rec fold : type a r. r -> <v : 'b. r -> 'b term -> r> -> a term -> r =
│ fun i f -> function
│ | Int _ as t -> f#v i t
│ | Add -> f#v i Add
│ | App (x, y) as t -> f#v (fold (fold i f x) f y) t
│
│ let v =
│ object method v : type a. _ -> a Gadt.term -> _ =
│ fun x -> function
│ | Int n -> x+n
│ | Add -> x+1
│ | App _ -> x+2
│ end
│
│ let r = Gadt.fold 0 v (App (App (Add, Int 3), Int 5))
└────
The point being that to match on a Gadt you will anyway need to use
the (type a) construct to allow refinement.
rixed asked and Ivan Gotovchits replied
───────────────────────────────────────
So there is no lighter syntax to specify that `f' should
accept any member of a GADT than the syntax to specify
that `f' should accept any type at all?
Only three methods of introducing rank-2 polymorphism are known to me:
1. records
2. objects
3. first-class modules
Jacques has demonstrated the solution with objects, which might be a
little bit more lightweight, at least as you don't need to define a
new data type beforehand. But the invocation is more verbose and
requires an annotation from the caller side, which could be
confusing. The third solution relies on first-class modules and is
even more verbose, at least on the definition side. Just for the sake
of completeness,
┌────
│ module type Visitor = sig
│ type t
│ val term : t -> 'a term -> t
│ end
│
│ let rec fold : type a r. r -> (module Visitor with type t = r) -> a term
│ -> r =
│ fun i ((module Visit) as f) t -> match t with
│ | Int _ as t -> Visit.term i t
│ | Add as t -> Visit.term i t
│ | App (x,y) as t ->
│ let i = fold i f x in
│ let i = fold i f y in
│ Visit.term i t
│
│ let s = fold 0 (module struct
│ type t = int
│ let term x _ = x + 1
│ end)
└────
And again, it is not about GADT. GADT act as a red herring here. As
I've demonstrated earlier, using a simple pair will suffice to display
the limitation of the prenex polymorphism. Even no ADT is required,
just apply one term to another two and you will get them unified,
e.g.,
┌────
│ let f g x y : unit = g x; g y
└────
will have type
┌────
│ val f : ('a -> unit) -> 'a -> 'a -> unit
└────
because 'a is quantified on the scope of `f' not `g', in other words,
it has type (not an OCaml syntax)
┌────
│ val f : forall 'a. ('a -> unit) -> 'a -> 'a -> unit
└────
while we would like to have a type
┌────
│ val f : forall 'b, 'c. (forall 'a. 'a -> unit) -> 'b -> 'c -> unit
└────
OCaml doesn't allow us to define types like `('a. 'a -> 'a)' and the
reason is not that it is hard to extend the parser it is…
I wonder, is this just a limitation of the OCaml parser or
is there some deep reason for these work-around (like is
the case, from my understanding, for the value
restriction)?
Yep, good catch! It is because of the impurity. Indeed, Haskell has
the Rank2Types extension that lets us write types like `(forall a. a
-> ()) -> b -> c -> ()', with no extra syntactic burden (modulo having
to provide the type annotation). But functions in Haskell are pure,
therefore it is possible. To make the story short and obvious, let me
do a simple demonstration of how things can go wrong in a language
with side-effects. Let's go back to the simple example of pairs and
the identity function. Consider the following nasty identity
function,
┌────
│ let bad_id () =
│ let cache = ref None in
│ fun x -> match cache.contents with
│ | None -> cache := Some x; x
│ | Some cache -> cache
└────
It has type `unit -> 'a -> 'a' therefore, if we would have the rank-1
polymorphism enabled for functions, we could apply it to the function
┌────
│ let map2 : fun ('a. 'a -> 'a) -> 'b -> 'c -> 'b * 'c = fun f (x,y) -> f x, f y
└────
as
┌────
│ let x,y : string * int = map2 (bad_id ()) "hello", 42
└────
and will get a segmentation fault, as `y' will now have type int but
hold a string.
And here comes the syntax as a savior as it lets us specify functions
that are guaranteed to be syntactic values. Indeed, all three
solutions syntactically guarantee that the provided argument is a
function, not a closure. Indeed, let's introduce the universal
identity via a record,
┌────
│ type id = { f : 'a. 'a -> 'a}
└────
and we can see that our `bad_id' is not accepted due to the value
restriction, while good_id, defined as,
┌────
│ let good_id x = x
└────
is perfectly fine, e.g.,
┌────
│ let id1 = {f = good_id} (*accepted *)
│ let id2 = {f = bad_id} (* rejected *)
└────
moreover, even a fine, but not syntactic, identity is also rejected
┌────
│ let fine_id () x = x
│ let id3 = {f = fine_id ()} (* rejected *)
└────
with the message
┌────
│ This field value has type 'b -> 'b which is less general than 'a. 'a -> 'a
└────
The same is true with modules,
┌────
│ module type Id = sig
│ val f : 'a -> 'a
│ end
│ module Id1 : Id = struct let f = good_id end (* accepted *)
│ module Id2 : Id = struct let f = bad_id () end (* rejected *)
│ module Id3 : Id = struct let f = fine_id () end (* rejected *)
└────
and with objects (left as an exercise).
To summarize, in order to enable rank2 polymorphism we need a special
kind of values to bear universal functions, as we can't rely on
ordinary functions, which could be constructed using partial
application. OCaml already had objects and records, which serve as a
fine media for universally quantified functions. Later first class
modules were introduced, which could also be used for the same
purpose. Probably, one could devise a special syntax (or rely on the
new attributes and extensions syntax, e.g., `map2 [%rank2 : fun x ->
x] ("hello",42)' but probably this will lead to an unnecessary
bloating of the language and the implementation, especially since we
already have three solutions with a more or less tolerable syntax (and
are in the base language, not an extension). Besides, if we will use
the `[@@unboxed]' annotation, or visitor will have the same
representation as a function, e.g.,
┌────
│ type 'r visitor = {visit : 'a. 'r -> 'a term -> 'r} [@@unboxed]
│ let count x _ = x + 1
│ let counter = {visit=count}
└────
and
┌────
│ # Core_kernel.phys_same count counter;;
│ - : bool = true
└────
Concerning rank-n polymorphism, in OCaml is is achieved using
functors. Yes, they are a little bit syntactically heavy and force us
to write signatures, but this is necessary anyway as rank-n is
undecidable (non-inferrable). Finally, as a real-world example [1] of
rank-2 polymorphism consider the universal WAVL tree that is a binary
tree with each element having a different type (aka heterogeneous
map). We use it in BAP as a backing store. You might find a few tricks
there, especially using continuation-passing in the recursive cases.
Cheers, Ivan
[1]:
<https://github.com/BinaryAnalysisPlatform/bap/blob/b40689e636607b977758af048b79d65684ce48c3/lib/knowledge/bap_knowledge.ml#L847-L1693>
Malcolm Matalka asked and Ivan Gotovchits replied
─────────────────────────────────────────────────
Why is type checking creating a record different than type
checking a function argument?
If we had the syntax (or something like it):
let map2 : ('a. 'a -> 'a) -> ('b * 'c) -> ('b * 'c)
Why would the type checker not be able to see that
map2 good_id ("hi", 42)
is valid but
map2 (fine_id ()) ("hi", 32)
is not, using the same logic that is verifying creating
the "id" record is not valid?
I believe it is possible, as it is possible in Haskell (with
RankNTypes and ScopedTypeVariables). The main (theoretical) difference
is that in OCaml we need to check whether an expression is expansive
and use a specialized generalization in case if it is (for the relaxed
value restriction). It will, however, complicate the type inference
engine a lot, but most importantly, changing the typing rule of
functions will have a tremendous impact on the language. So this would
be a very impractical solution. Especially, since we don't have the
mechanism of language extensions, enabling RankNTypes will make a lot
of programs untypeable, as they will now require type annotations
(recall that RankN is undecidable in general). It could probably be
implemented as a compiler command line parameter, like `-rectypes' but
this will be still quite impractical since more often code like `fun f
-> f 1, f true' is a programmer error, rather than a true request for
universal polymorphism (the same as with rectypes, recursive types a
more often an error rather than a deliberate attempt). Therefore,
enabling RankN(^1) polymorphism will type too many programs (not that
it is unsound, just many programs won't have sense) at the cost of
even more obscure type errors. On the other hand, we have three
syntactic constructs that let us express non-prenex polymorphism of
the necessary rank(^2) without breaking anything else. So it looks
like a good deal - we can have rankN polymorphism and decidable type
checker at the same time. Just think of polymorphic records/methods as
an embedded DSL for rankN polymorphism.
`==========' Footnotes:
1) An important point, that I forgot to notice, is that enabling
scoped
type variables, will inevitably enable rankN polymorphism, e.g., since
now any type could be a polytype, then suppose we have type
`'a. ('b.'b -> 'a) -> 'a' could be instantiated to 'a = 'd. ('c. ->
'd) -> 'd, so that our type is now `'d. ('b. 'b -> ('c. 'c -> 'd) ->
'd) -> ('c. 'c -> 'd) -> 'd' which is now rank3. Therefore, enabling
arbitrary quantification in the arrow type will lead to rankN and
immediately make undecidable most of the type checker.
1) We can craft arbitrary rank using records with universally
quantified
type variables, e.g., here is an example of rank3 polymorphism:
┌────
│ type 'a rank1 = {f1 : 's. 's -> 'a}
│ type 'a rank2 = {f2 : 'r. 'r -> 'a rank1}
└────
Indeed, `f2' has type `'a.('r. 'r -> ('s. 's -> 'a)'
OCamlPro's opam cheat sheet, with a new theme!
══════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/rfc-ocamlpros-opam-cheat-sheet-with-a-new-theme/4689/3>
Thomas Blanc announced
──────────────────────
The opam cheat-sheet is now published in its final form.
You can get the [colored] and [black-and-white] versions from our
website.
Happy hacking!
[colored]
<http://www.ocamlpro.com/wp-content/uploads/2019/11/ocaml-opam.pdf>
[black-and-white]
<http://www.ocamlpro.com/wp-content/uploads/2020/01/ocaml-opam-bw.pdf>
OCaml 4.10.0, first beta
════════════════════════
Archive: <https://discuss.ocaml.org/t/ocaml-4-10-0-first-beta/4989/1>
octachron announced
───────────────────
The release of OCaml 4.10.0 is approaching. We have published a first
beta version to help you adapt your software to the new features ahead
of the release.
During our preliminary tests for this new beta, we discovered that the
recent work towards a multicore-ready OCaml runtime introduced
compatibility issues within some opam packages, that were tweaking the
runtime internals. Most of those opam packages have been fixed, or
will be soon. Nevertheless, if you are affected by such compatibility
issue, please speak up.
The source code is available at these addresses:
<https://github.com/ocaml/ocaml/archive/4.10.0+beta1.tar.gz>
<https://caml.inria.fr/pub/distrib/ocaml-4.10/ocaml-4.10.0+beta1.tar.gz>
The compiler can also be installed as an OPAM switch with one of the
following commands.
┌────
│ opam switch create ocaml-variants.4.10.0+beta1 --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git
└────
or
┌────
│ opam switch create ocaml-variants.4.10.0+beta1+<VARIANT> --repositories=default,beta=git+https://github.com/ocaml/ocaml-beta-repository.git
└────
where you replace <VARIANT> with one of these:
• afl
• flambda
• fp
• fp+flambda
We want to know about all bugs. Please report them here:
<https://github.com/ocaml/ocaml/issues>
Happy hacking.
Kate added
──────────
For the people wanting to give OCaml 4.10.0beta1 a shot, here is an
opam overlay which adds fixes to major packages for them to work with
this beta: <https://github.com/kit-ty-kate/opam-alpha-repository>
To use it, simple call:
┌────
│ $ opam switch 4.10
│ $ opam repository add alpha git://github.com/kit-ty-kate/opam-alpha-repository.git
└────
Obviously, this repository should not be used in production and
probably contains a few bugs, but at least it allows everyone to have
almost as many packages available as with OCaml 4.09. Only 60ish
packages are still not available, but apart from the notable exception
of `merlin' all the essential packages and dependencies are there.
This work has been part of the release-readyness effort founded by the
OCaml Software Foundation as announced here:
<https://discuss.ocaml.org/t/ann-the-ocaml-software-foundation/4476/13>
The rest of the effort is going to be put towards having `merlin'
available for OCaml 4.10 and upstreaming all the fixes from
opam-alpha-repository (most of them have PRs associated already). I'm
hopeful for them be all upstreamed and available before the stable
release of OCaml 4.10.
Data engineer positions at Elastic, US/Canada/Western Europe (proximate to NA timezones)
════════════════════════════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/job-data-engineer-positions-at-elastic-us-canada-western-europe-proximate-to-na-timezones/4991/1>
Hezekiah Carty announced
────────────────────────
Our team here at [Elastic] has positions open for a few security data
engineers (aka wranglers of data and all the systems involved). We
are a distributed company so you don't have to be close to an office
to be considered. Infosec industry experience is _not_ required,
though of course welcome. We're surrounded by experts in the field so
you'll have lots of opportunities to learn as you go!
The official postings are available here (both have the same text and
only differ in title/seniority):
• Security data engineer -
<https://jobs.elastic.co/jobs/security-solutions/amer-distributed-/security-data-engineer/2005140#/>
• Senior security data engineer -
<https://jobs.elastic.co/jobs/security-solutions/amer-distributed-/security-senior-data-engineer/2005152#/>
Language-wise, OCaml/Reason makes up most of the code you’ll be
working on. Python makes up most of the rest, in particular taking
advantage of the machine learning and natural language processing
goodies that ecosystem provides. Most of the tools and service we
develop are internally focused, supporting security research and
improvements to security protections for our users. For those
so-inclined, there are lots of opportunities to present at and attend
conferences, present work in blog posts, contribute to open source
software projects and otherwise engage the community.
The positions are very similar to our [last hiring announcement],
though we had a different name at that point!
Please reach out to me if you have any questions. I’m available on the
OCaml or Reason Discord servers or by email at
hezekiah.carty@elastic.co.
[Elastic] <https://www.elastic.co/>
[last hiring announcement]
<https://discuss.ocaml.org/t/filled-posting-is-no-longer-open-threat-research-engineer-job-endgame-us/1937>
Release of naboris 0.1.0 a simple http server
═════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/release-of-naboris-0-1-0-a-simple-http-server/4994/1>
Shawn McGinty announced
───────────────────────
<https://github.com/shawn-mcginty/naboris>
I could use input on the API and the documentation. Working on trying
to improve both at the moment.
The goal was to create a very simple library for building RESTful type
of web servers. Make it _very_ easy to manage handle request/response
lifecycle and sessions.
In my opinion this type of web server is a great entry point for new
developers looking to explore the OCaml/Reason world.
Recently I have fallen in love with OCaml and Reason, and as a mostly
web centered developer I've found this area quite lacking. I'm still
new to the language and eco system so any guidance would be highly
appreciated!
Yawar Amin replied
──────────────────
Wow! It seems we had much the same idea–OCaml/Reason more accessible
to web developers new to the ecosystem :-D I've been working on
something very similar: <https://github.com/yawaramin/re-web/>
Ulrik Strid said
────────────────
There is also opium <https://github.com/rgrinberg/opium>
And morph <https://github.com/reason-native-web/morph> that has
similar goals.
It would be nice if we could either create a shared core that all
could build from or collaborate on one.
esy@0.6.0 release
═════════════════
Archive: <https://discuss.ocaml.org/t/ann-esy-0-6-0-release/5010/1>
Andrey Popp announced
─────────────────────
We've just released a new version of esy. You can install it with npm:
┌────
│ $ npm install -g esy@0.6.0
└────
[esy] is a package.json driven workflow for native development with
Reason/OCaml (and even C/C++). It provides per-project build
environments which are isolated from each other but share underlying
build caches so creating new environments is cheap.
While 0.6.0 is mainly about "quality-of-life" improvements it also got
few new features including a basic support for garbage collection of
unused build artifacts.
For more info see a [blog post] by @prometheansacrifice which
highlights important updates in 0.6.0.
[esy] <https://esy.sh>
[blog post] <https://esy.sh/blog/2020/01/12/0.6.0.html>
Old CWN
═══════
If you happen to miss a CWN, you can [send me a message] and I'll mail
it to you, or go take a look at [the archive] or the [RSS feed of the
archives].
If you also wish to receive it every week by mail, you may subscribe
[online].
[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
[RSS feed of the archives] <http://alan.petitepomme.net/cwn/cwn.rss>
[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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* [Caml-list] Attn: Development Editor, Latest OCaml Weekly News
@ 2020-01-21 14:09 Alan Schmitt
0 siblings, 0 replies; 12+ messages in thread
From: Alan Schmitt @ 2020-01-21 14:09 UTC (permalink / raw)
To: lwn, cwn, caml-list, comp
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Hello
Here is the latest OCaml Weekly News, for the week of January 14 to 21,
2020.
Table of Contents
─────────────────
How does the compiler check for exhaustive pattern matching?
resto 0.2 released
opam 2.0.6 release
soupault: a static website generator based on HTML rewriting
Spin: Project scaffolding tool and set of templates for Reason and OCaml
Old CWN
How does the compiler check for exhaustive pattern matching?
════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/how-does-the-compiler-check-for-exhaustive-pattern-matching/5013/1>
Dylan Irlbeck asked
───────────────────
Hi all. I'm relatively new to OCaml, and I was curious on how the
compiler is able to give a warning when a case list is non-exhaustive
- both from a high-level and, if possible, the implementation of this
check. I have some ideas about how one could do this, but none of my
ideas seem like they'd be nearly as efficient as the OCaml compiler
is.
gasche replied
──────────────
The canonical reference for exhaustivity-checking in OCaml is the
scientific publication
[Warnings for pattern matching] Luc Maranget 2007
The general idea is to consider all the patterns of a given
pattern-matching at once, generalize this structure to a "matrix" of
patterns (matching on several values in parallel), and devise an
algorithm to "explore" these pattern matrices in such a way that you
eventually tell if a given pattern-matrix is exhaustive, or can
propose a counter-example.
(I guess we should write a high-level/accessible blog post about
this.)
[Warnings for pattern matching]
<http://moscova.inria.fr/~maranget/papers/warn/index.html>
resto 0.2 released
══════════════════
Archive: <https://discuss.ocaml.org/t/ann-resto-0-2-released/5028/1>
Raphaël Proust announced
────────────────────────
On behalf on Nomadic Labs, I'm happy to announce the release of
version 0.2 of `resto', a library to create type-safe HTTP/JSON
services.
The library is available through opam (`opam install resto'),
distributed under LGPL, and hosted on
<https://gitlab.com/nomadic-labs/resto>.
`resto' was previously released as `ocplib-resto' maintained by
OCamlPro. The project is now maintained by Nomadic Labs.
Along with many bugfixes and a few added features, the main change of
this release is that the library is split into multiple packages with
fine-grained dependencies.
opam 2.0.6 release
══════════════════
Archive: <https://discuss.ocaml.org/t/ann-opam-2-0-6-release/5038/1>
R. Boujbel announced
────────────────────
We are pleased to announce the minor release of [opam 2.0.6].
This new version contains mainly build update & fixes. You can find
more information in this [blog post].
_opam is a source-based package manager for OCaml. It supports
multiple simultaneous compiler installations, flexible package
constraints, and a Git-friendly development workflow._
[opam 2.0.6] <https://github.com/ocaml/opam/releases/tag/2.0.6>
[blog post] <https://opam.ocaml.org/blog/opam-2-0-6>
soupault: a static website generator based on HTML rewriting
════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/ann-soupault-a-static-website-generator-based-on-html-rewriting/4126/11>
Daniil Baturin announced
────────────────────────
soupault 1.8.0 is [released] along with Lua-ML 0.9.1.
Lua-ML now raises `Failure' when Lua code execution fails. There's
much room for improvement in that area, for now I've just done
something that is better than just displaying errors on stderr but
otherwise allowing syntax and runtime errors pass silently.
If you have any ideas how perfect interpreter error reporting _should_
work, please share!
As of improvements in soupault itself, there's now:
• A way for plugins to specify their minimum supported soupault
version like `Plugin.require_version("1.8.0")'
• `TARGET_DIR' environment variable and `target_dir' Lua global that
contains the directory where the rendered page will be written, to
make it easier for plugins/scripts to place processed assets
together with pages.
• "Build profiles": if you add `profile = "production"' or similar to
widget config, that widget will be ignored unless you run `soupault
--profile production'.
• A bunch of new utility functions for plugins.
[released] <https://soupault.neocities.org/blog/soupault-1.8.0-release/>
Spin: Project scaffolding tool and set of templates for Reason and OCaml
════════════════════════════════════════════════════════════════════════
Archive:
<https://discuss.ocaml.org/t/spin-project-scaffolding-tool-and-set-of-templates-for-reason-and-ocaml/5047/1>
Mohamed Elsharnouby announced
─────────────────────────────
<https://github.com/tmattio/spin>
Old CWN
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[Alan Schmitt]
[send me a message] <mailto:alan.schmitt@polytechnique.org>
[the archive] <http://alan.petitepomme.net/cwn/>
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[online] <http://lists.idyll.org/listinfo/caml-news-weekly/>
[Alan Schmitt] <http://alan.petitepomme.net/>
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