Re: [Caml-list] let mutable (was OCaml Speed for Block Convolutions)

[Ohad Rodeh <orodeh@cs.huji.ac.il>]

I don't mean to barge into an open door here, but
the discussion here is about escape analysis. This certainly
does not require the new "mutable" syntax. My personal opinion
is that Caml has enough syntax as it is (try using/modifying the
OCaml mly files as an exercise ...). 

In any case, escape analysis a clever optimization allowing some heap
allocated objects to be allocated on the run-time stack.
The MLkit takes escape analysis into the extrem, using regions. Java
compilers also use escape analysis to reduce heap allocation. 

Since we are already on the "with list" thread, I'd like to add my 
own wish. I'm going to teach the "Purely Functional Data Structures" book
(Chris Okasaki) as a course next semester. To do the real nifty stuff, you
need to have polymorphic recursion supported by the compiler. Can this be
added to the next release? 

	Ohad.

On Fri, 8 Jun 2001, Jacques Garrigue wrote:

> About the introduction of a let mutable construct,
> Tom _ <tom7ca@yahoo.com> wrote
> 
> > 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.
> 
> Not exactly, the compiler may still need to build a reference.
> 
>   let mutable x = 0 in
>   List.iter (fun y -> x <- x+y) l;
>   x
> 
> Since x has tobe modified in a function called by iter, it must be
> wrapped into an actual reference cell.
> 
> As the compiler already does a good job at unboxing only locally used
> references, let mutable would only be some syntactic sugar (with
> exactly the same typing as a reference).
> 
> > Besides, the syntax is probably quite a bit more
> > natural to imperative programmers anyway.
> 
> This is actually the only argument for let mutable.
> I would also like such a construct, but I don't know whether its worth
> it. Thereal question is whether let mutable should be allowed at
> toplevel, with problems for both answers.
> 
> Cheers,
> 
> Jacques Garrigue
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