# JOURNAL-lex

## Session 1

Starting implementation of calc/lexer.py per lex.md plan.

Design choices:
- Token is a dataclass with `kind: str` and `value` (str | int | float | None)
- NUMBER tokens carry numeric value (int for integers, float for floats)
- All other tokens carry None value
- LexError subclasses Exception, message includes offending char and position

## Implementation results

Ran tests:
```
$ python -m unittest -q
....................
Ran 18 tests in 0.000s
OK
```

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

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

All DoD items satisfied. Claiming all gates D1-D4 together.