44 lines
1.3 KiB
Python
44 lines
1.3 KiB
Python
"""Evaluator for the calc AST.
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Result type rule: if the result is a whole number, return int; otherwise return float.
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Division is always true division. Division by zero raises EvalError.
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"""
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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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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 _coerce(-val)
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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 _coerce(left + right)
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if node.op == '-':
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return _coerce(left - right)
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if node.op == '*':
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return _coerce(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 _coerce(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)!r}")
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def _coerce(val: int | float) -> int | float:
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"""Return int if val is whole-valued, otherwise float."""
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if isinstance(val, float) and val.is_integer():
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return int(val)
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return val
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