# JOURNAL — Phase parse (Builder)

## 2026-06-15 — Start

Reading phase plan. Lex phase is DONE. Building parser on top of `calc/lexer.py`.

### Design

Grammar (recursive descent):
```
expr    → term   (('+' | '-') term)*
term    → unary  (('*' | '/') unary)*
unary   → '-' unary | primary
primary → NUMBER | '(' expr ')'
```

- `expr`/`term` loop = left-associative by construction
- `term` deeper than `expr` = `*`/`/` higher precedence than `+`/`-`
- `unary` recursive = right-associative unary (`--5` parses as `-(-5)`)

AST nodes:
- `Num(value)` — leaf
- `BinOp(op, left, right)` — binary operator
- `Unary(op, operand)` — unary operator

ParseError raised for: empty string, trailing operator, unclosed paren, consecutive numbers, mismatched parens.

## 2026-06-15 — Implementation + tests run

```
$ python -m unittest -q
Ran 35 tests in 0.001s
OK
```
(15 from test_lexer + 20 from test_parser)

Plan verify commands:
```
$ python -c "...parse(tokenize('1+2*3'))"
BinOp('+', Num(1), BinOp('*', Num(2), Num(3)))      # D1 ✓

$ python -c "...parse(tokenize('(1+2)*3'))"
BinOp('*', BinOp('+', Num(1), Num(2)), Num(3))       # D3 ✓

$ python -c "...parse(tokenize('8-3-2'))"
BinOp('-', BinOp('-', Num(8), Num(3)), Num(2))        # D2 ✓

$ python -c "...parse(tokenize('-5'))"
Unary('-', Num(5))                                     # D4 ✓

$ python -c "...parse(tokenize('3 * -2'))"
BinOp('*', Num(3), Unary('-', Num(2)))                # D4 ✓

$ python -c "...parse(tokenize('1 +'))"
calc.parser.ParseError: unexpected end of expression   # D5 ✓
```