evaluation order ...

evaluation order ...

[Pietro Abate]

Hi all,

#type ('a,'w) mt = ('a -> 'w) -> 'w
#let return a = fun k -> k a ;;
#let a = return 4 ;;
type ('a, 'b) mt = ('a -> 'b) -> 'b
val return : 'a -> ('a -> 'b) -> 'b = <fun>
val a : (int -> '_a) -> '_a = <fun>
#

# let b = a print_int;;
4val b : unit = ()

as expected ... but 

# let c = a id;;
This expression has type int -> int but is here used with type int -> unit

if I invert the order ...

#let a = return 4 ;;
val a : (int -> '_a) -> '_a = <fun>
#let c = a id;;;;
val c : int = 4
#let b = a print_int;;
This expression has type int -> unit but is here used with type int -> int
#

why does the order matter ?
if "val a" is of type (int -> '_a) -> '_a = <fun> why '_a is fixed as soon
as I use it once ? Do I have to add a type constraint ?

:)
p

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Re: [Caml-list] evaluation order ...

[Richard Jones]

On Tue, Jul 11, 2006 at 05:55:19PM +1000, Pietro Abate wrote:
> why does the order matter ?
> if "val a" is of type (int -> '_a) -> '_a = <fun> why '_a is fixed as soon
> as I use it once ? Do I have to add a type constraint ?

'_a isn't the same as 'a

There is a FAQ on this:

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

Rich.

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