36 lines
787 B
Python
36 lines
787 B
Python
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from typing import Generic, TypeVar, Optional, Callable
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T = TypeVar("T")
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class Thunk(Generic[T]):
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value: Optional[T]
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def __init__(self, func: Callable[[], T]):
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self.func = func
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self.value = None
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def get(self) -> T:
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if self.value is None:
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self.value = self.func()
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return self.value
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class Node:
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value: Thunk[int]
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class Add(Node):
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def __init__(self, left: Node, right: Node):
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self.value = Thunk(lambda: left.value.get() + right.value.get())
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class Mul(Node):
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def __init__(self, left: Node, right: Node):
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self.value = Thunk(lambda: left.value.get() * right.value.get())
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class Lit(Node):
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def __init__(self, num: int):
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self.num = num
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self.value = Thunk(lambda: num)
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if __name__ == "__main__":
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tree = Add(Mul(Lit(3), Lit(4)), Lit(5))
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print(tree.value.get())
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