[cwn] Attn: Development Editor, Latest OCaml Weekly News

[Alan Schmitt]

Hello,

Here is the latest OCaml Weekly News, for the week of April 14 to 21, 2015.

1) Suggested way to determine platform specific capabilities in build system?
2) OCaml-openmaple
3) Timeout
4) Other OCaml News

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1) Suggested way to determine platform specific capabilities in build system?
Archive: <https://sympa.inria.fr/sympa/arc/caml-list/2015-04/msg00082.html>
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** Malcolm Matalka asked and Daniel Bünzli replied:

> What is the current suggested way to determine what, roughly, autoconf
> would do for you? I have some platform specific functionality to be
> included (or excluded) depending on the OS.

I don't know if there's a suggested way but here are various ways to proceed.

If you are using ocamlbuild, you can use `Sys.win32` since 4.01.0 or
`Sys.os_type = "Win32"` to determine if you are on windows and otherwise get
the (stripped and lowercased) result of `uname -s`, see e.g (but it's missing
the win bit):

<https://github.com/dbuenzli/tsdl/blob/master/myocamlbuild.ml#L6>

If you are using Makefiles you may want include
`$(ocamlc -where)/lib/ocaml/Makefile.config` and use the `$SYSTEM` variable.

If this is only needed for C stubs you can also try solve this at the CPP
level ? but I guess this can be quite brittle ? see e.g (here again missing
the win bit as it's undefined for now):

<https://github.com/dbuenzli/mtime/blob/master/src-os/mtime_stubs.c#L11-L21>

In any case make sure the value can be overridden from the command line for
cross compilation scenarios.
      
** Thomas Gazagnaire then added:

See also the system detection functions in opam-depext:

<https://github.com/ocaml/opam-depext/blob/master/depext.ml#L76>
      
** Ivan Gotovchits also suggested:

oasis, look at setup.data and setup.ml
      
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2) OCaml-openmaple
Archive: <https://sympa.inria.fr/sympa/arc/caml-list/2015-04/msg00089.html>
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** Maxence Guesdon announced:

I started OCaml-openmaple, bindings to the Openmaple C library:
  <https://github.com/zoggy/ocaml-openmaple>

This is still work in progress but you can give it a try.
It uses the excellent OCaml-ctypes library.
      
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3) Timeout
Archive: <https://sympa.inria.fr/sympa/arc/caml-list/2015-04/msg00099.html>
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** Rodolphe Lepigre asked and Benjamin Greenman:

> I was wondering: is there a standard way to stop a computation after, say,
> a given number of milliseconds (or seconds) in OCaml?
> 
> For instance I would like to have a function
> 
> exception Timeout
> val exec : int -> ('a -> 'b) -> 'a -> 'b
> 
> such that [exec t f x] computes [f x] but raises [Timeout] in case the
> computation did not end before [t] milliseconds (or seconds).
> 
> My guess would be that I need to use some Unix signals magic. Has anyone
> come up with a clean solution to this problem?

Here's a small function I use, taken from the book "Developing Applications
with Objective Caml"
<http://caml.inria.fr/pub/docs/oreilly-book/html/book-ora168.html>

exception Timeout
let sigalrm_handler = Sys.Signal_handle (fun _ -> raise Timeout)
let timeout (time : int) (f : 'a -> 'b) (arg : 'a) =
   let old_behavior = Sys.signal Sys.sigalrm sigalrm_handler in
   let reset_sigalrm () = ignore (Unix.alarm 0); Sys.set_signal Sys.sigalrm old_behavior in
   ignore (Unix.alarm time) ;
   let res = f arg in reset_sigalrm () ; res
      
** Rodolphe Lepigre then said:

Great, thank you!

I only see one problem: when [Timeout] is raised, the signal handler is not
reset. This can be fix by doing something like:

  try let res = f arg in reset_sigalrm (); res
  with e -> (reset_sigalrm (); raise e)

This will have the advantage of transmitting other exceptions to the caller
as well.

Also, I guess [Unix.alarm time] should also be in the [try ... with ...].
      
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4) Other OCaml News
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** From the ocamlcore planet blog:

Thanks to Alp Mestan, we now include in the OCaml Weekly News the links to the
recent posts from the ocamlcore planet blog at <http://planet.ocaml.org/>.

Mid/Senior Software Development Engineer at Lookingglass Cyber Solutions (Full-time):
  <http://functionaljobs.com/jobs/8810-mid-senior-software-development-engineer-at-lookingglass-cyber-solutions>

Senior/Principal Software Development Engineer at Lookingglass Cyber Solutions (Full-time):
  <http://functionaljobs.com/jobs/8809-senior-principal-software-development-engineer-at-lookingglass-cyber-solutions>
      
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