38 lines
1.1 KiB
Python
38 lines
1.1 KiB
Python
from __future__ import annotations
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from calc.parser import BinOp, Node, Num, Unary
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class EvalError(Exception):
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pass
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def evaluate(node: Node) -> int | float:
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"""Walk an AST and return its numeric value.
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Result type rule: integer arithmetic stays int; true division always
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produces a float (callers display whole-valued floats without '.0').
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"""
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if isinstance(node, Num):
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return node.value
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if isinstance(node, Unary):
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val = evaluate(node.operand)
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if node.op == '-':
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return -val
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raise EvalError(f"unknown unary operator: {node.op!r}")
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if isinstance(node, BinOp):
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left = evaluate(node.left)
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right = evaluate(node.right)
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if node.op == '+':
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return left + right
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if node.op == '-':
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return left - right
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if node.op == '*':
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return left * right
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if node.op == '/':
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if right == 0:
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raise EvalError("division by zero")
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return left / right
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raise EvalError(f"unknown binary operator: {node.op!r}")
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raise EvalError(f"unknown node type: {type(node)!r}")
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