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To: skaller@ozemail.com.au
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] tpyping question
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Date: Mon, 11 Aug 2003 11:46:15 +0900
From: Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp>
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From: skaller <skaller@ozemail.com.au>

> type x = [`A | `B of int | `V of float];;
> let g (a:x) = a;;
> let f a = match a with
> | `A -> g a
> (* | `B _ *) | _ -> g a;;
> 
> Compiles fine, but gives an error if the comments are
> removed.

Indeed, there seems to be a bug here, since the non-commented version
should be equivalent to

# let f a = match a with
  | `A ->  g a
  | `B _ -> g a
  | _ -> g a;;
val f : x -> x = <fun>

I will investigate this.
On the other hand, this code is meaningless, as _ is more general
than `B _, and the order of or-patterns is not significant.

If the code you really intended was

  let f a = match a with
    | `A ->  g a
    | `B _ -> g a

then the answer is in the manual:

  let f = function `A | `B _ as a -> g a

Jacques Garrigue

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