# Journal — lex phase

## Build run

Implemented `calc/lexer.py` with:
- `Token` dataclass with `kind` (str) and `value` (int | float | str | None)
- `LexError(Exception)` for invalid characters
- `tokenize(src: str) -> list[Token]` scanning char-by-char

Design choices:
- `Token` is a plain dataclass so later phases (parser, evaluator) can pattern-match on `.kind`
- Numbers: scanned greedily while char is digit or `.`; cast to `int` if no `.` in raw string, else `float`
- Operators stored as their literal char as `value` (handy for error messages)
- EOF always appended as final token (parser-friendly sentinel)

## Test run output

```
$ python -m unittest -q
..............
----------------------------------------------------------------------
Ran 14 tests in 0.000s

OK
```

## Verify commands output

```
$ 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
```