# JOURNAL — Phase eval (Builder)

## 2026-06-15 — Implementation

Built evaluator, CLI, and test suite in one pass.

AST walk in `calc/evaluator.py`:
- `Num`: return `node.value` (int or float as stored by lexer)
- `Unary('-')`: negate result of recursive evaluate
- `BinOp('+'/'-'/'*')`: straightforward arithmetic on evaluated children
- `BinOp('/')`: true division; guard `right == 0` → `EvalError`; if result is float and whole, return `int(result)` (D3 rule)

D3 result type rule: `evaluate()` returns `int` for whole-valued results, `float` for non-whole. This means `4/2` → `int(2)` (prints `2`), `7/2` → `float(3.5)` (prints `3.5`). Pure integer arithmetic stays int throughout (Python int + int = int).

CLI `calc.py`: catches `LexError`, `ParseError`, `EvalError` → stderr + exit 1. No traceback exposed.

Test run: 46 tests pass (15 lexer + 20 parser + 11 evaluator). No regressions.

Verified all plan cases:
```
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 to stderr, exit 1
python calc.py "1 +"     → error to stderr, exit 1
```