Re: [Caml-list] ocaml and concurrency

[Brian Hurt <bhurt@spnz.org>]

On Fri, 30 Jan 2004, Martin Berger wrote:

> > Perhaps because you're a type theorist? <g>
> 
> being a type theorist has many disadvantages ...
> 
> > C not only *does* have function types, it has
> > first class function values just like ML does.
> 
> well, i'm not so sure about this for two reasons.

Technically, he's correct.  What C doesn't have is partial function 
application, which makes having functional types much less worthwhile- 
it's impossible for a function type to also contain state.  Which is why 
when I do callbacks in C, I always include a void * context which is 
passed (uninspected) to the callback routine.

I mean, writting this function in C would be interesting to say the least:

let summer ival =
    let cval = ref ival in
    let f x = cval := !cval + x; !cval in
    f
;;

C's type syntax also discourages you from using pointers to functions.  
I've been programming C way too long, I can just dash out prototypes like:

extern int (*)(int (*)(int), int) foo(int (*)(int (*)(int), int), int);

I can parse them too, although normally I *would* use typedefs.  The ocaml 
equivelent type:
((int -> int) -> int -> int) -> int -> ((int -> int) -> int -> int)
is easier to read and easier to type and parse.

> 
> firstly, NULL-pointers (i'm assuming that in C/C++ function
> pointers can be NULL, though it's been too long for me to remember
> precisely). 

They can.  You can even cast integer values to be function pointers- and I 
have, legitimately (hint: BIOS functions).  I've also debugged bugs where 
wild pointers where clobbering function pointers, and boy wasn't that fun.  

I'm not sure I'd compare NULL to variant types.  It's more like a 
standardized abuse of C's concept of a pointer.

-- 
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                                - Gene Spafford 
Brian

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