45 lines
1.4 KiB
Python
45 lines
1.4 KiB
Python
"""Evaluator: walks an AST (from calc.parser) and returns int | float.
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Result-type rule: if the result is whole-valued (no fractional part), return int;
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otherwise return float. This means 4/2 → 2 (int) and 7/2 → 3.5 (float).
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"""
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from __future__ import annotations
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from calc.parser import Num, BinOp, Unary, Node
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class EvalError(Exception):
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pass
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def _normalize(v: int | float) -> int | float:
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if isinstance(v, float) and v == int(v):
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return int(v)
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return v
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def evaluate(node: Node) -> int | float:
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if isinstance(node, Num):
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return _normalize(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 _normalize(-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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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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return _normalize(result)
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raise EvalError(f"unknown node type: {type(node).__name__}")
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