Can I specialize a type in a signature using types before that type and in the signature? Here is an example:
signature A = sig
type t
type s
end
Can I specialize A by the following?
signature B = A where type s = t list
Both SML/NJ and Mlton complain that t is unbound.
No, that indeed cannot be done directly. The reasons are rather technical, it is not easy to ascribe a well-behaved semantics to such an operation in the general case.
The closest you can get is by introducing another auxiliary type:
signature B =
sig
type t'
include A with type t = t' with type s = t' list
end
