Re: [Caml-list] OCaml Speed for Block Convolutions

[Tom _ <tom7ca@yahoo.com>]

--- William Chesters <williamc@paneris.org> wrote:
> Hugo Herbelin writes:
>  > Assume more generally that you can modify any
> local variable as in the
>  > (standard) following example:
>  > 
>  > let fact (mutable n) =
>  >   let mutable r = 1 in
>  >   while n > 0 do
>  >      r <- r * n;
>  >      n <- n - 1
>  >   done;
>  >   r
> 
> This doesn't actually make life much easier for the
> compiler.  On 32-bit machines [see other thread!], 
> `r' must be a reference (in the 
> C++ sense) to a heap object---64-bit float, plus
> header.

I don't see why. The compiler has full type 
information.  All it may have to do is box up
a return value.

In any case, whether or not the compiler in the
current implementation can or cannot do good type
inference and may or may not be forced to box
a floating point number, the two constructs mean
something different to the programmer, and they
behave differently.  In particular "mutable x"
can never be passed around as a reference, while
"x = ref ..." can.  If not anything else, that
prevents the programmer from inadvertently inhibiting
a compiler optimization by passing around a reference.

Besides, the syntax is probably quite a bit more 
natural to imperative programmers anyway.

Tom.


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