# JOURNAL — Phase `lex`

## Implementation notes

### Design choices
- Used `@dataclass` for `Token` to get `__eq__` and `__repr__` for free — useful in tests.
- Number parsing: scan while char is digit or `.`; if `.` in raw string → `float()`, else `int()`. Handles `42`, `3.14`, `.5`, `10.`.
- Single-char operators: dict lookup for O(1) dispatch.
- LexError message includes both the character (quoted) and its 0-based position.

### Test run (verified locally)
```
$ python -m unittest -q
Ran 14 tests in 0.000s
OK

$ python -c "from calc.lexer import tokenize; print([(t.kind,t.value) for t in tokenize('3.5*(1-2)')])"
[('NUMBER', 3.5), ('STAR', '*'), ('LPAREN', '('), ('NUMBER', 1), ('MINUS', '-'), ('NUMBER', 2), ('RPAREN', ')'), ('EOF', None)]

$ python -c "from calc.lexer import tokenize; tokenize('1 @ 2')"
Traceback (most recent call last):
  ...
calc.lexer.LexError: unexpected character '@' at position 2
```