# JOURNAL — phase `parse`

## 2026-06-15 — Initial implementation

Plan: recursive-descent parser with two precedence levels.
- `expr` → additive level (+ -)
- `term` → multiplicative level (* /)
- `unary` → handle leading -
- `primary` → NUMBER or parenthesized expr

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

Left-associativity achieved naturally by the while loop in `expr` and `term`.

## Test run output
```
Ran 36 tests in 0.001s
OK
```

## AST shape verification
```
1+2*3: BinOp(op='+', left=Num(value=1), right=BinOp(op='*', left=Num(value=2), right=Num(value=3)))
8-3-2: BinOp(op='-', left=BinOp(op='-', left=Num(value=8), right=Num(value=3)), right=Num(value=2))
8/4/2: BinOp(op='/', left=BinOp(op='/', left=Num(value=8), right=Num(value=4)), right=Num(value=2))
(1+2)*3: BinOp(op='*', left=BinOp(op='+', left=Num(value=1), right=Num(value=2)), right=Num(value=3))
-5: Unary(op='-', operand=Num(value=5))
-(1+2): Unary(op='-', operand=BinOp(op='+', left=Num(value=1), right=Num(value=2)))
3*-2: BinOp(op='*', left=Num(value=3), right=Unary(op='-', operand=Num(value=2)))
```

## Error cases
```
'1 +': ParseError: unexpected end of input
'(1': ParseError: expected RPAREN, got 'EOF' (None)
'1 2': ParseError: unexpected token 'NUMBER' (2) after expression
')(': ParseError: unexpected token 'RPAREN' (')')
'': ParseError: empty expression
```