49 lines
1.5 KiB
Python
49 lines
1.5 KiB
Python
"""Evaluator for the arithmetic AST produced by calc.parser.
|
|
|
|
evaluate(node) -> int | float
|
|
|
|
Whole-valued results are returned as int ("4/2" -> 2).
|
|
Non-whole results are returned as float ("7/2" -> 3.5).
|
|
Division by zero raises EvalError.
|
|
"""
|
|
from __future__ import annotations
|
|
|
|
from calc.parser import Node, Num, BinOp, Unary
|
|
|
|
|
|
class EvalError(Exception):
|
|
pass
|
|
|
|
|
|
def _normalize(val: int | float) -> int | float:
|
|
"""Return int if val is a whole-valued float, otherwise unchanged."""
|
|
if isinstance(val, float) and val.is_integer():
|
|
return int(val)
|
|
return val
|
|
|
|
|
|
def evaluate(node: Node) -> int | float:
|
|
"""Walk an AST node and return its numeric value."""
|
|
if isinstance(node, Num):
|
|
return node.value
|
|
if isinstance(node, BinOp):
|
|
l = evaluate(node.left)
|
|
r = evaluate(node.right)
|
|
if node.op == '+':
|
|
return _normalize(l + r)
|
|
if node.op == '-':
|
|
return _normalize(l - r)
|
|
if node.op == '*':
|
|
return _normalize(l * r)
|
|
if node.op == '/':
|
|
if r == 0:
|
|
raise EvalError("division by zero")
|
|
return _normalize(l / r)
|
|
raise EvalError(f"unknown operator {node.op!r}")
|
|
if isinstance(node, Unary):
|
|
val = evaluate(node.operand)
|
|
if node.op == '-':
|
|
return _normalize(-val)
|
|
raise EvalError(f"unknown unary operator {node.op!r}")
|
|
raise EvalError(f"unknown AST node type {type(node).__name__!r}")
|