type ('a) mylist = Cons of 'a * ('a) mylist | Nil
And you won't have any of the kinds of difficulties we're discussing here with that. It's just that some of the topics we're exploring in this course press against the walls where things are hard (or sometimes not even possible) to do in OCaml (and sometimes Haskell too).
+
+By the way, this issue about not-enough-polymorphism doesn't arise in Haskell. Here are the Church numerals:
+
+ > type Church a = (a -> a) -> a -> a
+ > let { zero :: Church a; zero = \s z -> z; one :: Church a; one = \s z -> s z; succ n = \s z-> s (n s z) }
+ > let two = succ one
+ > two ('S':) "0"
+ "SS0"
+ > :t two
+ two :: (a -> a) -> a -> a
+ > two (1+) 0
+ 2
+
+The reason that OCaml has trouble here where Haskell doesn't has to do with some fundamental differences between their type systems, that we haven't yet explored. (Specifically, it has to do with the fact that OCaml has *mutable reference cells* in its type system, and this obliges it to place limits on where it generalizes type variables, else its type system becomes inconsistent.)