yield only works inside a for — a while-loop generator does not compile

def gen(n: int):
    i = 0
    while i < n:
        yield i          # error: undefined variable (yield)
        i = i + 1

The same generator written with for i in range(n): yield i also fails today, so the working surface is narrower than the "for-in/yield" support suggests — worth establishing exactly which shape does work before starting.

yield reported as an "undefined variable" says it is not being recognised as a statement at all in this position, so the parse arm is keyed to a context rather than the keyword.

Found by sweeping generator/ternary/unpacking constructs against CPython.

Recon 2026-07-31 — bigger than the title suggests, not attempted

Measured, not assumed: grep -n "'yield'" compiler/pyparser.inc returns ZERO matches. yield is not recognised ANYWHERE in the NilPy frontend today — not "works inside for, fails inside while" as the title implies, but unimplemented full stop. Confirmed directly: for i in range(n): yield i (the shape the title says already works) ALSO fails with the same "undefined variable (yield)" — matching the ticket body's own footnote, not the title.

CurProcIsGenerator/CurGenSelfSym/GenTryDepth and the "stackful coroutine body" machinery mentioned around PyParseDef (pyparser.inc) exist for a Pascal-only ; generator; directive — there is no NilPy-side wiring to it, automatic or otherwise. So this isn't a parse-context bug to relocate; it's full Python generator support to build: recognising a yield-containing def as a generator automatically, giving it suspend/ resume semantics (there IS a coroutine backend to potentially reuse, just not connected), and the iteration protocol (for x in gen(), list(gen())) on top. Sized like the other bigger, dedicated-pass features in this backlog (feature-nilpy-lambda-compiled-closure, closure-ABI items), not like a quick bug fix. Not attempted this session — retitling the fork correctly (unimplemented feature, not a narrow context bug) is the useful output of this recon.

Gate

make test-nilpy + self-host byte-identical, plus generators driven by while, by for ... in range, and by for ... in <list>, each consumed by a for loop and by list().