# 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)
```