43 lines
1.2 KiB
Python
43 lines
1.2 KiB
Python
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):
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"""Walk the AST and return int | float.
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Result-type rule: if the value is whole (n == int(n)), return int; else float.
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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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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).__name__!r}")
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def _coerce(value):
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"""Return int if value is whole, float otherwise."""
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if isinstance(value, float) and value == int(value):
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return int(value)
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return value
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