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[Caml-list] inference and phantom types
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Date: -- (:)
From: Julien Cohen <jcohen@l...>
Subject: [Caml-list] inference and phantom types
I read in the thread 
http://caml.inria.fr/archives/200109/msg00097.html
that phantom types could be used in ocaml but I have some 
troubles understanding the way they really work.

In the following session I use a phantom type ('a,'b)t to 
simulate a list with an additionnal type 'b. I create a special 
cons preserving the type. I create an (int,bool)t value and when 
I make a cons on it and the phantom type seems not to be well 
infered:



         Objective Caml version 3.04

# type ('a,'b) t = 'a list;;
type ('a, 'b) t = 'a list

# let f (x:'a) (y:('a,'b) t) = (x::y : ('a,'b) t);;
val f : 'a -> ('a, 'b) t -> ('a, 'b) t = <fun>

# let (v: (int,bool) t) = [1];;
val v : (int, bool) t = [1]

# f 1 v;;
- : (int, '_a) t = [1; 1]


Is there a fundamental reason for the bool type not to be inferred?
(no response in the ocaml-beginner list)

Thanks
Julien Cohen

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