[Caml-list] GADT and weak polymorphism

[Runhang Li <runhang@posteo.net>]

Hi, camels

Consider the following module:

    module HList = struct

      type (_, _) hlist =
        | Empty : ('a, 'a) hlist
        | Cons  : 'c * ('a, 'b) hlist -> ('c -> 'a, 'b) hlist

      let cons : type a b c. c -> (a, b) hlist -> (c -> a, b) hlist =
        fun h tl -> Cons (h, tl)

      let empty = Empty

      let ( **> ) = cons

      let l = '2' **> "str" **> empty

    end

The type of ``l`` is ``(char -> string -> ‘_a, ‘_a) hlist``. I would like to know the reason that weak polymorphism shows up here.

Thank you


Kindly,

Runhang