Polymorphic variant typing
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Date:   (:) 
From:  Gilles Dubochet <dubochet@u...> 
Subject:  Polymorphic variant typing 
Hello everyone, The following O'Caml expression: let incr g x = match x with  `Int i > `Int (i+1)  x > (g x);; Receives type: (([> `Int of int ] as 'a) > ([> `Int of int ] as 'b)) > 'a > 'b Why? I am quite astonished. I would have expected a type more like: ([> ] > [> ]) > [> `Int of int ] > [> `Int of int ] or in Wand or Rémylike row variable notation with which I am a little more comfortable (I am not exactly sure the preceding type is correct in the 'at leat  at most' notation of O'Caml): ([ 'a ] > [ 'b ]) > [ `Int of int  'a ] > [ `Int of int  'b ] Could anyone be kind enough to give me some clues about where to look at to find an explanation or even better, explain me what is going on? I am particularly puzzled by the fact that the g function's *argument* type is 'at least `Int of int'. This rejects the following code which seems intuitively correct: incr (function `Float f > `Float (f+.1.));; Thank you. Cheers, Gilles.