# JOURNAL — eval phase

## Implementation run (2026-06-16)

### Pre-state
- 44 tests passing (lex + parse phases)
- `calc/lexer.py`, `calc/parser.py` already in place
- AST nodes: `Num(value)`, `BinOp(op, left, right)`, `Unary(op, operand)`

### calc/evaluator.py

Wrote tree-walking `evaluate(node)`:
- `Num` → return `node.value`
- `Unary` → `-evaluate(operand)` (only `-` is supported)
- `BinOp` → recurse left/right, apply op; `/` case: raise `EvalError("division by zero")` when `right == 0`, otherwise `left / right`
- Whole-float normalisation: `if isinstance(result, float) and result.is_integer(): return int(result)`

### calc/test_evaluator.py

12 tests across 4 classes:
- `TestArithmetic` — the 5 DoD examples
- `TestDivision` — true division, div-by-zero as `EvalError`, no bare `ZeroDivisionError`
- `TestResultType` — `4/2` is `int`, `7/2` is `float`, plain int arithmetic stays `int`, negative whole is `int`

### calc.py (CLI)

At repo root; uses `sys.argv[1]`, calls lex→parse→eval pipeline. Catches `LexError | ParseError | EvalError`, prints `error: {e}` to stderr, exits 1. Clean exit 0 on success.

### Test run
```
$ python -m unittest -q
Ran 56 tests in 0.001s
OK
```

### CLI smoke test
```
$ 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 "8-3-2"    → 3
$ python calc.py "-2+5"     → 3
$ python calc.py "2*-3"     → -6
$ python calc.py "1/0"      → error: division by zero  (exit 1)
$ python calc.py "1 +"      → error: unexpected token 'EOF' (None)  (exit 1)
```

All DoD items satisfied. Writing ## DONE to STATUS-eval.md.