## help with type inference - ayuda con inferencia de tipos

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• I had thinking about this and I can t find the solution : What means _a list maybe something like ( a a) list ????? # (function x - function y - x@y) [];; -
Message 1 of 2 , Dec 7, 2003

What means '_a list maybe something like ('a'a) list ?????

# (function x -> function y -> x@y) [];;
- : '_a list -> '_a list = <fun>

# (function x -> function y -> x@y) [] 1;;
This expression has type int but is here used with type 'a list

Well I supose it's the same tha 'a list -> 'a list

Is this true??? If so why caml say the first expresion has type
'_a list -> '_a list. It looks a nosense

How he/she inference this type for this expresion??

Thanks
• ... The meaning of _a is explained here: http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html#variables_de_types_faibles Rich. -- Richard Jones.
Message 2 of 2 , Dec 8, 2003
On Mon, Dec 08, 2003 at 05:37:07AM -0000, wences_correo wrote:
>
> What means '_a list maybe something like ('a'a) list ?????
>
> # (function x -> function y -> x@y) [];;
> - : '_a list -> '_a list = <fun>
>
>
> # (function x -> function y -> x@y) [] 1;;
> This expression has type int but is here used with type 'a list
>
> Well I supose it's the same tha 'a list -> 'a list
>
> Is this true??? If so why caml say the first expresion has type
> '_a list -> '_a list. It looks a nosense
>
> How he/she inference this type for this expresion??

The meaning of '_a is explained here:

http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html#variables_de_types_faibles

Rich.

--
Richard Jones. http://www.annexia.org/ http://freshmeat.net/users/rwmj
Merjis Ltd. http://www.merjis.com/ - improving website return on investment
C2LIB is a library of basic Perl/STL-like types for C. Vectors, hashes,
trees, string funcs, pool allocator: http://www.annexia.org/freeware/c2lib/
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