]> On Wed, 19 Nov 2003, 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;; This is untypeable. What's the type of f? It's a function that takes a 'a and returns a function which takes a type 'a and returns a function which takes a type 'a and returns a function which takes a type 'a and etc. What you want is List.fold_left, which has type: ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a and can be implemented as: let rec fold_left f init_val = function | [] -> init_val | h :: t -> fold_left f (f init_val h) t ;; But don't reimplement it, use the library version. > > let add x y = x + y;; > let x = apply add [2; 3];; > print_int x;; let x = List.fold_left (+) 0 [2; 3];; You don't need to define a special add function. -- "Usenet is like a herd of performing elephants with diarrhea -- massive, difficult to redirect, awe-inspiring, entertaining, and a source of mind-boggling amounts of excrement when you least expect it." - Gene Spafford Brian ------------------- To unsubscribe, mail caml-list-request@inria.fr Archives: http://caml.inria.fr Bug reports: http://caml.inria.fr/bin/caml-bugs FAQ: http://caml.inria.fr/FAQ/ Beginner's list: http://groups.yahoo.com/group/ocaml_beginners