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[Caml-list] Closure & Ref
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Date: 2003-11-17 (21:30)
From: chris.danx <chris.danx@n...>
Subject: Re: [Caml-list] Closure & Ref
Brian Hurt wrote:

> Since you're not setting the reference, why have one?  Instead, try:
> let prodAdd x = fun y -> x + y
> But we can do it simpler than that:
> let prodAdd x y = x + y
> And use partial function application.  (prodAdd 4) returns a function 
> which adds 4 to whatever int parameter passed to it.

I didn't know OCaml had partial function application, thanks!  I have 
programmed in Haskell before, but never got seriously into it (the 
things I wanted to do like IO where "advanced" in Haskell, whereas 
they're basic to me.  That's one reason I want to learn OCaml, it 
doesn't so hard to do trivial interaction).

> This allows you to have multiple different lists being constructed 
> independently.  Note, the above code is actually more generic than it 
> looks- I had to add an explicit type statement to make it "come out 
> correct".  Without the explicit type information:
> let make_listacc () =
>         let r = ref [] in
>         let acc x = r := x :: !r
>         and lst () = !r
>         in acc, lst
> ;;
> The function is both clearer than the original, and creates lists of any 
> type, not just ints.  If you hear me bitching about C++ and Java making 
> generics "special and extraordinary", this is a classic example of what 
> I'm kvetching about.

I hear you.  From my previous spell in FP I really got to like the ease 
of "generics" which are inconvient in C++ and a pain in Ada.  GUIs and 
IO was just easier.


> If you want to access specific members of a list (other than the head), I
> wouldn't recommend using a list, but instead some other datastructure (an
> array or hash table being the obvious choices).

It was just a toy example to see if I could get that aspect of this idea 
to work in OCaml.  Hmm...


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