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[Caml-list] Typing problem with polymorphic variants
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Date: -- (:)
From: Alessandro Baretta <alex@b...>
Subject: [Caml-list] Typing problem with polymorphic variants
This just baffles me.

 > Values do not match:
 >   val feature :
 >     [> `Clear | `Length of int | `Pitch of int
 >               | `Width of 'a] -> string
 > is not included in
 >   val feature : [> `Clear] -> string

Why are "match-anything" functions of the kind of

let f = function
   | `Foo -> "foo"
   | `Bar -> "bar"
   | _ -> "?"

incompatible with signatures like

val f : [> `Foo ] -> string
?


There clearly is no case when a value of type [> `Foo] will 
not be acceptable for f. So why does the type checker reject 
this?

Alex

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