# JOURNAL — parse phase

## Session 1 (2026-06-16)

Starting parse phase. Lex phase complete (11 tests green).

### Design: recursive-descent parser

Grammar chosen:
```
expr    := term  (('+' | '-') term)*
term    := unary (('*' | '/') unary)*
unary   := '-' unary | primary
primary := NUMBER | '(' expr ')'
```

Why iterative (not right-recursive) for expr/term: gives natural left-associativity.
Why unary is right-recursive: `-` chains right, e.g. `--5` = `-(-(5))`.

### Test run results (2026-06-16)

```
python -m unittest -v
Ran 35 tests in 0.001s
OK
```

All 24 parser tests + 11 lexer tests green on first attempt.

Verified shapes:
- `1+2*3` → `BinOp('+', Num(1), BinOp('*', Num(2), Num(3)))` ✓ D1
- `8-3-2` → `BinOp('-', BinOp('-', Num(8), Num(3)), Num(2))` ✓ D2
- `(1+2)*3` → `BinOp('*', BinOp('+', Num(1), Num(2)), Num(3))` ✓ D3
- `-5` → `Unary('-', Num(5))` ✓ D4
- `3 * -2` → `BinOp('*', Num(3), Unary('-', Num(2)))` ✓ D4
- `1 +` → `ParseError: unexpected end of input` ✓ D5

AST nodes (dataclasses):
- `Num(value: int | float)` — leaf
- `BinOp(op: str, left: Node, right: Node)` — binary operation
- `Unary(op: str, operand: Node)` — unary minus (op='-')