43 lines
1.3 KiB
Python
43 lines
1.3 KiB
Python
"""Evaluator for arithmetic AST nodes produced by calc.parser."""
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from calc.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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"""Walk the AST and return the numeric result.
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Whole-valued floats are returned as int (e.g. 4/2 → 2, not 2.0).
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Division by zero raises EvalError.
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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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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 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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result = left + right
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elif node.op == "-":
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result = left - right
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elif node.op == "*":
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result = left * right
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elif node.op == "/":
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if right == 0:
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raise EvalError("division by zero")
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result = left / right
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else:
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raise EvalError(f"unknown operator: {node.op!r}")
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# Normalize: whole-valued float → int
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if isinstance(result, float) and result == int(result):
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return int(result)
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return result
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raise EvalError(f"unknown node type: {type(node).__name__}")
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