]> >>>>> "sj" == Scott J <jscott@planetinternet.be> writes: sj> What is meant by first first-class polymorphism? First class polymorphism in this case lets you define values with polymorphic types at levels other than the top level, like so: type foo = { test : 'a 'b . ('a -> 'b) -> 'a list -> 'b list } let a = { test = List.map } # a.test;; - : ('a -> 'b) -> 'a list -> 'b list = <fun> # a.test ((+) 1) [3; 5; 7];; - : int list = [4; 6; 8] # a.test ((^) "a") ["a"; "b"; "c"];; - : string list = ["aa"; "ab"; "ac"] For objects, this allows you to define a list type, complete with map method, as an object. For example: class ['a] clist x = object method map : 'b . ('a -> 'b) -> 'b list = fun f -> List.map f x end let a = new clist [1;2;3] let b = new clist ["a";"b";"c"] # a #map (fun x -> x + 1);; - : int list = [2; 3; 4] # b #map (fun x -> x ^ "-");; - : string list = ["a-"; "b-"; "c-"] (Note: this is a very uninteresting definition if a list class, but it should show you the kind of thing you can now do.) John. ------------------- 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