Browse thread
[Caml-list] C++ STL and template features compared with OCaml parametric polymorphism and OO features
[
Home
]
[ Index:
by date
|
by threads
]
[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: | 2004-09-30 (10:13) |
From: | Keith Wansbrough <Keith.Wansbrough@c...> |
Subject: | Re: [Caml-list] Factoring HOFs [was Re: C++ STL...] |
> Yipes! Ok, so I'm missing some typing subtlety. Why does this end up with a > single polymorphic type: > > # let map_2 m g f x = m g (m f x);; > val map_2 : ('a -> 'b -> 'b) -> 'a -> 'a -> 'b -> 'b = <fun> You want it to have type (forall 'a 'b 'f. ('a -> 'b) -> ('a 'f -> 'b 'f)) -> ('b -> 'c) -> ('a -> 'b) -> 'a 'f -> 'b 'f but OCaml doesn't allow nested quantifiers (i.e., higher-rank polymorphism). It actually wouldn't be very hard to support, if you're prepared to accept the need for the occasional type annotation - see http://research.microsoft.com/~simonpj/papers/putting/index.htm. --KW 8-) ------------------- 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