44 lines
1.3 KiB
Python
44 lines
1.3 KiB
Python
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 evaluate(node: Node) -> int | float:
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"""Walk the AST and return the numeric result."""
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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 -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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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 operator: {node.op!r}")
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raise EvalError(f"unknown node type: {type(node)!r}")
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def fmt_result(v: int | float) -> str:
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"""Format a result for display.
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Rule: whole-valued floats (e.g. 2.0 from 4/2) print without a trailing .0;
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non-whole floats print normally; integers print as integers.
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"""
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if isinstance(v, float) and v.is_integer():
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return str(int(v))
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return str(v)
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