On 19.11.2003 19:54, Peter Scott wrote:

> I'm having an interesting disagreement with ocaml about types. I'm 
> trying to make a function to imitate the lisp apply function. That is, I 
> want to make a function which will apply another function to a list.
> 
> I came up with this code:
> 
> let rec apply f args =
>   match args with
>       arg :: rest -> apply (f arg) rest
>     | [] -> f;;
> 
> let add x y = x + y;;
> let x = apply add [2; 3];;
> print_int x;;
> 
> As you can see, the idea is to go recursively applying the function to 
> the first element of the list. Unfortunately, I get this message when 
> run: "This expression has type 'a but is here used with type 'b -> 'a", 
> referring to the "(f arg)" part.
> 
> Is there a way around this?

Well, note that your "apply" function would only make sense for 
fixed-length lists (e.g. "apply add [2; 3; 4]" is not right). In OCaml, 
fixed-length lists are called "tuples". ;-)

-- 
Aleksey Nogin

Home Page: http://nogin.org/
E-Mail: nogin@cs.caltech.edu (office), aleksey@nogin.org (personal)
Office: Jorgensen 70, tel: (626) 395-2907

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