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