# JOURNAL-eval — Builder

## 2026-06-15 — Implementation

### What was built

- `calc/evaluator.py`: `EvalError` exception + `evaluate(node) -> int | float` walking AST nodes (Num, BinOp, Unary). Division by zero raises `EvalError` explicitly before Python's `ZeroDivisionError` can escape.
- `calc.py` (root): CLI entry point. Calls `tokenize → parse → evaluate`. `_fmt()` converts whole-valued floats to int display.
- `calc/test_evaluator.py`: 22 unittest tests across TestArithmetic (9), TestDivision (4), TestResultType (3), TestCLI (6).

### Test run

```
$ python -m unittest -q
Ran 68 tests in 0.224s
OK
```

### CLI spot-checks

```
$ 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 (exit 1)
$ python calc.py "1 +"       → error: unexpected token 'EOF' (None) (exit 1)
```

All match DoD expected values.

### Design notes

- `evaluate` always returns `int` for integer operations and `float` for true division. The `_fmt` function in `calc.py` handles D3 display: floats that are whole become int strings.
- `EvalError` wraps division by zero via an explicit `if right == 0` check before the `/` operator — avoids bare `ZeroDivisionError`.