Re: [Caml-list] Pattern matching

[Pixel <pixel@mandrakesoft.com>]

"Diego Olivier Fernandez Pons" <FernandezPons@iFrance.com> writes:

[...]

> let couples = function n ->
>   let rec couplesCPS = function
>     | (n,_) -> [ ]

vs

> let couples = function n ->
>   let rec couplesCPS = function
>     | (i,_) when (i = n) -> [ ]

the problem is an expressivity one. Something like 

(function A(e) -> e | _ -> ...) 

become dependent on the context: is there a variable "e" in the surrounding
context. This is not good.

One could add some sugar allowing:

> let couples = function n ->
>   let rec couplesCPS = function
>     | (@@n,_) -> [ ]

where @@n force the scope of n to be non-local. But too much sugar makes the
language harder to learn :)

[...]

> let egalite = function
>    | (x,x) -> true
>    | (x,y) -> false
> ;;
> # This variable is bound several times in this matching

i wonder why this one is not allowed since it can't have any other meaning
than the one it has in prolog. What's the reason for not having it rewritten
to:

> let egalite = function
>    | (x,x') when x=x' -> true
>    | (x,y) -> false

maybe you're right than the kind of equality (= vs ==) may be the problem...
-------------------
Bug reports: http://caml.inria.fr/bin/caml-bugs  FAQ: http://caml.inria.fr/FAQ/
To unsubscribe, mail caml-list-request@inria.fr  Archives: http://caml.inria.fr