35 lines
1.1 KiB
Python
35 lines
1.1 KiB
Python
"""Evaluator: walks the AST produced by calc.parser and returns a numeric result."""
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from __future__ import annotations
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from .parser import Num, BinOp, Unary
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class EvalError(Exception):
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pass
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def evaluate(node) -> int | float:
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"""Recursively evaluate an AST node and return int or float."""
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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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operand = evaluate(node.operand)
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if node.op == "-":
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return -operand
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raise EvalError(f"unknown unary op: {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 op: {node.op!r}")
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raise EvalError(f"unknown node type: {type(node).__name__!r}")
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