nac3-spec/toy-impl/inference.py

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from type_def import *
def find_subst(ctx: dict[str, Type],
sub: dict[str, Type],
a: Type,
b: Type):
"""
Find substitution s such that ctx(a) = s(sub(ctx(b)))
return error message if type mismatch
"""
# is error
if isinstance(sub, str):
return sub
if isinstance(a, TypeVariable) and a.name in ctx:
a = ctx[a.name]
if isinstance(b, TypeVariable):
if b.name in ctx:
b = ctx[b.name]
elif b.name in sub:
b = sub[b.name]
else:
if len(b.constraints) > 0:
if isinstance(a, TypeVariable):
if len(a.constraints) == 0:
return f"{b} cannot take value of an unconstrained variable {a}"
diff = [v for v in a.constraints if v not in b.constraints]
if len(diff) > 0:
over = ', '.join([str(v) for v in diff])
return f"{b} cannot take value of {a} as {a} can range over [{over}]"
else:
if a not in b.constraints:
return f"{b} cannot take value of {a}"
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if a == b:
return sub
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if b in a.get_vars():
return "Recursive type is not supported"
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sub[b.name] = a
return sub
if isinstance(a, TypeVariable):
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if a == b:
return sub
else:
return f"{a} can take values other than {b}"
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if isinstance(a, BotType):
return sub
if type(a) == type(b):
if isinstance(a, ParametricType):
old = sub
for x, y in zip(a.params, b.params):
old = find_subst(ctx, old, x, y)
return old
elif isinstance(a, ClassType) or isinstance(a, PrimitiveType):
if a.name == b.name:
return sub
elif isinstance(a, VirtualClassType):
return find_subst(a.base, b.base)
else:
raise Exception()
return f"{a} != {b}"