Re: [Caml-list] Polymorphic variant typing

["Olivier Pérès" <olivier.peres@laposte.net>]

Gilles Dubochet a écrit :

> let incr g x = match x with
>     | `Int i -> `Int (i+1)
>     | x -> (g x);;
> 
> Receives type:
> (([> `Int of int ] as 'a) -> ([> `Int of int ] as 'b)) -> 'a -> 'b

    Now, how about this :

let incr x g = match x with
   | `Int i -> `Int (i+1)
   | x -> g x;;

    Doesn't it look like your code ? OCaml 3.08.2 types it as follows :
val incr : ([> `Int of int ] as 'a) -> ('a -> ([> `Int of int ] as 'b)) 
-> 'b = <fun>

    This is more like it !

incr (`Int 1) (fun (`Int i) -> (`Int (i+1)));;
- : [> `Int of int ] = `Int 2

incr (`Float 1.0) (fun x -> match x with (`Float f) -> (`Float (f +. 
1.0)) | x -> x);;
- : [> `Float of float | `Int of int ] = `Float 2.

    It remains to understand why the type of incr should depend upon the 
order in which the arguments are given...

    Yours,

    Olivier.