Re: [Caml-list] still silly issues on polymorphic types

[Thibault Suzanne <thi.suzanne@gmail.com>]

Le 27/09/2011 20:43, Walter Cazzola a écrit :
> On Tue, 27 Sep 2011, Christophe Papazian wrote:
>
>>> uhm, I have a couple of questions I don't understand on your
>>> explanation:
>>> - why the most general type is int->'a and not 'a -> 'b?
>
>> Because if I need a function of type int -> 'a I can give a function 
>> of type 'a -> 'b.
>> But if I need a function of type 'a -> 'b I can not use a function of 
>> type int -> 'a.
>> So int -> 'a is more general and 'a -> 'b is more specific.
>
>> General rule : if a < b then (a->c) > (b->c)
>
> probably this is a question whose answer will be RTFM but I'll try to
> get your mercy (;-)): what define that a is lesser than b? is there a
> table of the precendece among types?
>
Disclaimer : I'm not at all an expert and i discovered these things with 
these mails. But if I've understood, "a is lesser than b" means that 
when a function expects an argument of type 'b, a value of type 'a can 
be given to this function. For an example, List.length can take a value 
of type int list, because int list < 'a list. If I remember, in fact, 'a 
< 'b if a value of type 'a is also a value of type 'b.