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Date: Thu, 12 Dec 2002 14:17:42 -0800
Subject: Re: [Caml-list] Resource acquisition is initialization
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From: Quetzalcoatl Bradley <qbradley@blackfen.com>
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On Thursday, December 12, 2002, at 05:15  AM, Xavier Leroy wrote:
> For a mutex:
>
> let synchronize mut action =
>   try
>     Mutex.lock mut;
>     let res = action () in
>     Mutex.unlock mut;
>     res
>   with x ->
>     Mutex.unlock mut;
>     raise x
>
> You get the idea.

For fun I try to use campl4 to add synchronize directive.

usage:   synchronize "expression that evaluates to Mutex.t" in 
"expression"
The value is result of "expression".

  Example:

let lock = Mutex.create ();;
let counter = ref 0;;
let next_sym prefix =
   synchronize lock in
     let current = !counter in
       counter := current + 1;
       prefix ^ (string_of_int current)
;;

synchronize.ml file:

open Pcaml;;

EXTEND
  expr: LEVEL "expr1"
   [[ "synchronize"; e1 = expr; "in"; e2 = expr ->
    <:expr<
     let __synchronize_lock = $e1$ in
     do {
      Mutex.lock __synchronize_lock;
     try
      let __synchronize_result = $e2$ in
      do { Mutex.unlock __synchronize_lock; __synchronize_result }
     with z ->
      do { Mutex.unlock __synchronize_lock; raise z }
     }
    >>
   ]];
END;;
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