# JOURNAL — eval phase

## Build

1. Read `calc/parser.py` and `calc/lexer.py` to understand AST node contracts
   (`Num`, `BinOp`, `Unary`) and `Token`/`ParseError` types.

2. Wrote `calc/evaluator.py`:
   - `EvalError(Exception)` wraps all evaluation failures.
   - `evaluate(node)` walks the AST recursively.
   - Division by zero raises `EvalError("division by zero")`.
   - Result-type rule: `float.is_integer()` → cast to `int`; otherwise keep `float`.

3. Wrote `calc.py` (top-level CLI):
   - Accepts exactly one argument (the expression string).
   - Chains `tokenize → parse → evaluate`, prints result.
   - Catches `LexError | ParseError | EvalError`, prints `error: <msg>` to stderr, exits 1.
   - No traceback surfaces.

4. Wrote `calc/test_evaluator.py` (unittest):
   - `TestArithmetic` — D1: +, -, *, /, precedence, parens, unary minus.
   - `TestDivision` — D2: true division, `EvalError` on /0, confirms no bare `ZeroDivisionError`.
   - `TestResultType` — D3: `4/2 → int(2)`, `7/2 → float(3.5)`.
   - `TestCLI` — D4: subprocess smoke tests for valid and invalid CLI invocations.

## Verification

All plan Verify commands run from a clean working directory:

```
python -m unittest -q       → Ran 51 tests, OK
python calc.py "2+3*4"      → 14   (exit 0)
python calc.py "(2+3)*4"    → 20   (exit 0)
python calc.py "7/2"        → 3.5  (exit 0)
python calc.py "4/2"        → 2    (exit 0, no trailing .0)
python calc.py "1/0"        → error: division by zero  (exit 1, stderr)
python calc.py "1 +"        → error: unexpected end of expression  (exit 1, stderr)
```

Additional D1 edge cases verified:
```
python calc.py "8-3-2"      → 3
python calc.py "-2+5"       → 3
python calc.py "2*-3"       → -6
```

All DoD gates confirmed PASS. Committed as f083f901.