MLton has a flag, -show-basis <file>, that causes MLton to pretty print to file the basis defined by the input program. For example, if foo.sml contains
fun f x = x + 1
then mlton -show-basis foo.basis foo.sml will create foo.basis with the following contents.
val f: int -> int
If you only want to see the basis and do not wish to compile the program, you can call MLton with -stop tc.
Displaying signatures
When displaying signatures, MLton prefixes types defined in the signature them with _sig. to distinguish them from types defined in the environment. For example,
signature SIG =
sig
type t
val x: t * int -> unit
end
is displayed as
signature SIG =
sig
type t
val x: _sig.t * int -> unit
end
Notice that int occurs without the _sig. prefix.
MLton also uses a canonical name for each type in the signature, and that name is used everywhere for that type, no matter what the input signature looked like. For example:
signature SIG =
sig
type t
type u = t
val x: t
val y: u
end
is displayed as
signature SIG =
sig
type t
type u = _sig.t
val x: _sig.t
val y: _sig.t
end
Canonical names are always relative to the "top" of the signature, even when used in nested substructures. For example:
signature S =
sig
type t
val w: t
structure U:
sig
type u
val x: t
val y: u
end
val z: U.u
end
is displayed as
signature S =
sig
type t
val w: _sig.t
val z: _sig.U.u
structure U:
sig
type u
val x: _sig.t
val y: _sig.U.u
end
end
Displaying structures
When displaying structures, MLton uses signature constraints wherever possible, combined with where type clauses to specify the meanings of the types defined within the signature. For example:
signature SIG =
sig
type t
val x: t
end
structure S: SIG =
struct
type t = int
val x = 13
end
structure S2:> SIG = S
is displayed as
signature SIG =
sig
type t
val x: _sig.t
end
structure S: SIG
where type t = int
structure S2: SIG
where type t = S2.t