# JOURNAL — phase: lex

## 2026-06-15 — Start

Read phase plan. Mission: build `calc/lexer.py` with `tokenize()`, Token type, LexError, and unittest suite.

Plan:
- Token: dataclass with `kind` (str) and `value` (int | float | None)
- Kinds: NUMBER, PLUS, MINUS, STAR, SLASH, LPAREN, RPAREN, EOF
- LexError: custom Exception with char + position
- tokenize(): iterate over chars, match numbers (int/float), operators, parens; skip whitespace; raise LexError on unknown char; append EOF at end

## 2026-06-15 — Implementation

Created:
- `calc/__init__.py` (empty package marker)
- `calc/lexer.py` — token scanner using manual char-by-char iteration
- `calc/test_lexer.py` — 22 unittest cases

Float parsing design: detect float vs int by presence of `.` in scanned substring. Handle `.5` (leading dot) and `10.` (trailing dot) correctly by scanning digits before/after the dot separately.

## 2026-06-15 — Test run

```
$ python -m unittest -q
----------------------------------------------------------------------
Ran 22 tests in 0.001s

OK
```

## 2026-06-15 — Verify commands

```
$ python -c "from calc.lexer import tokenize; print([(t.kind,t.value) for t in tokenize('42')])"
[('NUMBER', 42), ('EOF', None)]

$ python -c "from calc.lexer import tokenize; print([(t.kind,t.value) for t in tokenize('3.14')])"
[('NUMBER', 3.14), ('EOF', None)]

$ python -c "from calc.lexer import tokenize; print([(t.kind,t.value) for t in tokenize('.5')])"
[('NUMBER', 0.5), ('EOF', None)]

$ python -c "from calc.lexer import tokenize; print([(t.kind,t.value) for t in tokenize('10.')])"
[('NUMBER', 10.0), ('EOF', None)]

$ python -c "from calc.lexer import tokenize; print([t.kind for t in tokenize('1+2*3')])"
['NUMBER', 'PLUS', 'NUMBER', 'STAR', 'NUMBER', 'EOF']

$ 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')" 2>&1
calc.lexer.LexError: unexpected character '@' at position 2
```

All plan verify commands produce expected output. Claiming D1–D4.