NilPy arithmetic/ordering dunders — umbrella

Python's operator overloading (__add__, __lt__, …) is the same feature as Pascal's operator + overload syntax, already supported for Pascal. This is the NilPy side of it. Split out of [[bug-nilpy-dunder-protocols-ignored-fall-back-to-handle-arithmetic]] via [[decide-nilpy-arithmetic-dunder-scope]] (DECIDED 2026-08-01: phased, low risk first).

Today C(1) + C(2) on two tyClass operands takes the raw IR_BINOP path and adds the instance pointers — silent, no error, a different plausible number every run.

Phasing (the decision)

1. [[bug-nilpy-comparison-dunders-not-dispatched]] — __lt__/__eq__/ __gt__/etc. No existing special-cased class-operand route on </> today, so no collision risk. Covers the most likely real use (sorted()/min()/max() on custom-ordered objects). Do this first.
2. [[feature-nilpy-arithmetic-dunders-full-protocol]] — __add__ etc. Bigger: has to compose per-operator with existing special-cased class-operand routes (e.g. Path("a") / "b" for pathlib) without breaking any of them. Do after (1), one operator at a time.

Gate

make test-nilpy + self-host byte-identical, .npy per dunder vs CPython's own output. No matching dunder → genuine runtime TypeError (matching PyNotContainerError/PyNotCallableError/PyNoSetitemError), never a silent handle-arithmetic result.

2026-08-09 — both phases complete; umbrella resolved

• Phase 1, [[bug-nilpy-comparison-dunders-not-dispatched]] — done (in done/).
• Phase 2, [[feature-nilpy-arithmetic-dunders-full-protocol]] — done today. Direct, reflected and in-place forms of + - * / // % **, then __divmod__ as its last named gap.

Re-measured at HEAD rather than taken on trust, since this ticket's own opening paragraph (C(1) + C(2) adding instance pointers) is a PRE-WORK snapshot and had been stale for a week: + - * / // % ** and __radd__ all match CPython, and the umbrella's Gate condition — no matching dunder gives a genuine runtime TypeError rather than silent handle arithmetic — holds.

Explicitly NOT covered, tracked separately and deliberately left open:

• [[bug-nilpy-matmul-operator-does-not-parse]] — @ has no infix token (p20).
• [[bug-nilpy-power-augmented-assign-does-not-parse]] — **=, same shape.
• [[decide-nilpy-runtime-dunder-dispatch-mechanism]] — operands reached as runtime variants through a container or parameter. Note that the __eq__, __lt__/__gt__ and __divmod__ work landed 2026-08-08/09 supplies a worked mechanism for exactly that (PyUserObjBoolDunder / PyUserObjObjDunder over the class RTTI), so that decision now has an implementation to point at rather than a blank page.
• [[bug-nilpy-static-typed-operands-skip-mixed-type-guard]] — mismatched static pairs computing instead of raising.

Log

• 2026-08-09 — resolved, commit dc2e5b46f.