momonorphisation and imperative/weak type variables

[Stephen Weeks]

Here is the example I promised yesterday.  It type checks under imperative or
weak type variables, but not the value restriction.  With our usual
monomorphisation strategy, we would duplicate the definitions of f and g,
causing r to be incremented twice, instead of once.

val r = ref 13
val f: unit -> 'a -> 'a = fn () => (r := !r + 1; fn x => x)
val g: 'a -> 'a = f()
val _ = g "foo"
val _ = g true