JOURNAL — eval phase

Implementation run (2026-06-16)

Pre-state

44 tests passing (lex + parse phases)
calc/lexer.py, calc/parser.py already in place
AST nodes: Num(value), BinOp(op, left, right), Unary(op, operand)

calc/evaluator.py

Wrote tree-walking evaluate(node):

Num → return node.value
Unary → -evaluate(operand) (only - is supported)
BinOp → recurse left/right, apply op; / case: raise EvalError("division by zero") when right == 0, otherwise left / right
Whole-float normalisation: if isinstance(result, float) and result.is_integer(): return int(result)

calc/test_evaluator.py

12 tests across 4 classes:

TestArithmetic — the 5 DoD examples
TestDivision — true division, div-by-zero as EvalError, no bare ZeroDivisionError
TestResultType — 4/2 is int, 7/2 is float, plain int arithmetic stays int, negative whole is int

calc.py (CLI)

At repo root; uses sys.argv[1], calls lex→parse→eval pipeline. Catches LexError | ParseError | EvalError, prints error: {e} to stderr, exits 1. Clean exit 0 on success.

Test run

$ python -m unittest -q
Ran 56 tests in 0.001s
OK

CLI smoke test

$ python calc.py "2+3*4"    → 14
$ python calc.py "(2+3)*4"  → 20
$ python calc.py "7/2"      → 3.5
$ python calc.py "4/2"      → 2
$ python calc.py "8-3-2"    → 3
$ python calc.py "-2+5"     → 3
$ python calc.py "2*-3"     → -6
$ python calc.py "1/0"      → error: division by zero  (exit 1)
$ python calc.py "1 +"      → error: unexpected token 'EOF' (None)  (exit 1)

All DoD items satisfied. Writing ## DONE to STATUS-eval.md.

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