nadji@noos.fr writes:

| Hi all,
| 
| I am puzzled by the code below which doesn't work.
| 
| # let f = function `B -> ();;
| val f : [ `B] -> unit = <fun>
| # let g x = match (x:[`A|`B]) with `A -> () | y -> f y;;
| Characters 51-52:
|   let g x = match (x:[`A|`B]) with `A -> () | y -> f y;;
|                                                      ^
| This expression has type [ `A | `B] but is here used with type [ `B]
| (denoting the "y" from the "f y")
| 
| How can I say to OCaml that "y" can't be of type `A ?

Try

# let g x = match (x:[`A|`B]) with `A -> () | `B as y -> f y;;

Dan

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