compiler question

compiler question

[Michael Wohlwend]

Hi,

I executed the following code,  the array a0 was allocated to match the 
filesize and get32 reads 4 bytes via input_byte:

  let idx = ref 0 in
  try
    while true do
      a0.(!idx) <-get32 file;
      incr idx;
    done
  with
    End_of_file -> close_in file;


this code works as bytecode but gives an array exception when compiled to 
native code. Is the execution order different on the two compilers? The a0.
(!idx) get evaluted before the get32 in native-code, but with bytecode the 
get32 is computed first (it seems).
The code works if I add a temporary variable like:
let t = get32 file in
a0.(!idx) <- t;

is this a feature ? :-)
cheers,
 Michael

Re: [Caml-list] compiler question

[Richard Jones]

On Sat, Jul 22, 2006 at 09:19:15PM +0200, Michael Wohlwend wrote:
>   let idx = ref 0 in
>   try
>     while true do
>       a0.(!idx) <-get32 file;

You shouldn't rely on the order that these are executed.  Normal
parameter evaluation (which this is not) in OCaml happens to be right
to left, but it's not defined to be that way.  Use the let binding if
you depend on a particular ordering.

> let t = get32 file in
> a0.(!idx) <- t;

Rich.

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Richard Jones, CTO Merjis Ltd.
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