51 lines
1.4 KiB
Python
51 lines
1.4 KiB
Python
"""
|
|
AST evaluator for the calc expression language.
|
|
|
|
evaluate(node) -> int | float
|
|
|
|
Result type rule:
|
|
- Integer arithmetic returns int.
|
|
- Division (/) always uses true division; if the result is whole-valued
|
|
(e.g. 4/2 == 2.0) it is coerced to int, otherwise returned as float.
|
|
"""
|
|
|
|
from calc.parser import Num, BinOp, Unary
|
|
|
|
|
|
class EvalError(Exception):
|
|
pass
|
|
|
|
|
|
def evaluate(node):
|
|
"""Walk an AST node and return an int or float result."""
|
|
if isinstance(node, Num):
|
|
return node.value
|
|
|
|
if isinstance(node, Unary):
|
|
val = evaluate(node.operand)
|
|
if node.op == '-':
|
|
return -val
|
|
raise EvalError(f"Unknown unary operator: {node.op!r}")
|
|
|
|
if isinstance(node, BinOp):
|
|
left = evaluate(node.left)
|
|
right = evaluate(node.right)
|
|
if node.op == '+':
|
|
result = left + right
|
|
elif node.op == '-':
|
|
result = left - right
|
|
elif node.op == '*':
|
|
result = left * right
|
|
elif node.op == '/':
|
|
if right == 0:
|
|
raise EvalError("Division by zero")
|
|
result = left / right
|
|
else:
|
|
raise EvalError(f"Unknown binary operator: {node.op!r}")
|
|
# Coerce whole-valued floats to int so "4/2" prints as "2" not "2.0"
|
|
if isinstance(result, float) and result.is_integer():
|
|
return int(result)
|
|
return result
|
|
|
|
raise EvalError(f"Unknown AST node type: {type(node).__name__!r}")
|