JOURNAL — Phase eval

Implementation notes

evaluator.py

Built evaluate(node) -> int | float walking Num, BinOp, Unary nodes.

Num: returns node.value (already int or float from lexer)
Unary('-'): returns -evaluate(operand) recursively
BinOp(+,-,*): straightforward arithmetic (Python int+int=int)
BinOp(/): true division via left / right; checks right == 0 → EvalError; if result == int(result) → return int(result) (D3 rule), else return float

D3 rule: after true division, 4/2 = 2.0; 2.0 == int(2.0) is True, so return int(2.0) = 2. 7/2 = 3.5; 3.5 != 3, so return 3.5 (float).

calc.py

Top-level CLI at repo root. Imports from calc.*. Catches LexError, ParseError, EvalError → prints to stderr, exits 1. Traceback never escapes.

test_evaluator.py

26 new tests across D1–D4 categories:

D1 (arithmetic): 11 tests including all DoD examples plus edge cases
D2 (division): 4 tests including EvalError-not-ZeroDivisionError check
D3 (result type): 5 tests including str() formatting
D4 (CLI): 6 tests using subprocess

Verification output (local)

python -m unittest -q
Ran 63 tests in 0.228s
OK

python calc.py "2+3*4"    → 14
python calc.py "(2+3)*4"  → 20
python calc.py "7/2"      → 3.5
python calc.py "4/2"      → 2
python calc.py "1/0"      → error: division by zero (stderr, exit 1)
python calc.py "1 +"      → error: unexpected token 'EOF' (None) (stderr, exit 1)

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