def define_nat_adt(prelude):
"""Defines a Peano (unary) natural number ADT.
Zero is represented by z(). s(n) adds 1 to a nat n.
Adds the fields nat, z, and s to the preluide, representing
(respectively) the nat ADT and the z and s constructors.
"""
prelude.nat = GlobalTypeVar("nat")
prelude.z = Constructor("z", [], prelude.nat)
prelude.s = Constructor("s", [prelude.nat()], prelude.nat)
prelude.mod[prelude.nat] = TypeData(prelude.nat, [], [prelude.z, prelude.s])
def test_type_call():
tc = TypeCall(GlobalTypeVar("tf"), [TupleType([])])
check_visit(tc)
def test_type_data():
td = TypeData(GlobalTypeVar("td"), [TypeVar("tv")], [])
check_visit(td)
def test_global_type_var():
gtv = GlobalTypeVar("gtv")
check_visit(gtv)
def test_type_data():
td = TypeData(GlobalTypeVar('td'), [TypeVar('tv')], [])
check_visit(td)