Two small observations

From: William Chesters (
Date: Sat Oct 23 1999 - 19:32:14 MET DST

Date: Sat, 23 Oct 1999 18:32:14 +0100
Message-Id: <199910231732.SAA04758@toy.william.bogus>
From: William Chesters <>
Subject: Two small observations

`with' is not fully polymorphic. For instance, in

        type 'a t = { length: int; elt: int -> 'a }

        let map: ('a -> 'b) -> 'a t -> 'b t =
          fun f t -> { t with elt = f t.elt }

the inferred type for map is given by

        val map : ('a -> 'a) -> 'a t -> 'a t

I can see that this is a simple way out of the problem of what to say
if a `with' changes fields in a way inconsistent with the others'
types, but it is a little confusing.

   The other thing is that the compiler doesn't tell you if your type
annotations turn out to be over-optimistic, like that on `map' above.
It would be nice to have the option of having it generate a warning in
these cases.

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