map(lambda ...) is unimplemented and filter does not exist
list(map(lambda v: v + 1, [1, 2]))
# error: Nil Python: map() over lambda is not implemented (int, str and float are)
list(filter(lambda v: v > 1, [1, 2, 3]))
# error: undefined variable (filter)
map exists but only with a TYPE as the first argument (map(int, ...));
filter is absent entirely. Both fail at compile time, so nothing computes a
wrong answer — filed as a feature.
The callable-value machinery this needs is already in place: a lambda in a
name, a lambda in a list, and a lambda passed to a Callable[...] parameter
all work today, and sorted already works. So this is wiring two builtins to
the existing runtime dispatcher rather than new infrastructure. sorted(key=)
and min/max with a key= are the same shape and worth doing in the same
pass.
Found by the functions/closures sweep against CPython.
Mostly already fixed — verified 2026-07-31; ONE gate case still segfaults
map/filter over a lambda AND a named def, each consumed by list() and
by a for loop, already landed (via pymap_call/pyfilter_call in
pyeval.pas, reached from ordinary compiled code, not just exec()) and all
match CPython exactly — re-measured directly, not assumed.
The ticket's own third gate case does NOT work: map(c.double, xs) (a
BOUND METHOD as the callable) SEGFAULTS. Root cause: pymap_call/
pyfilter_call's key parameter is typed Pointer (8 bytes) — a bound
method is a {code, receiver} PAIR (16 bytes), so passing one through
truncates the receiver half. This is the SAME representation gap as
[[bug-nilpy-bound-method-cannot-pass-through-a-callable-parameter]]
(already investigated and deferred this session as needing a careful,
multi-call-site pass through PyAnnTypeAt's parameter-vs-field typing) —
not a separate bug, just another call site hitting the identical limit.
Left OPEN rather than closed: fixing the shared representation issue fixes
both at once, so this ticket stays a live pointer to that gap rather than
being marked done on the strength of 2 out of 3 shapes.
Added test/test_nilpy_map_filter_lambda_def.npy covering the WORKING
shapes (lambda, def, both via list() and for) so they have direct
regression coverage; the bound-method crash is NOT asserted there (it
would turn a segfault into a test-harness crash) — it stays reproducible
via this ticket's own repro until the representation fix lands.
Gate
make test-nilpy + self-host byte-identical, plus map/filter over a
lambda, a named def and a bound method, each consumed by list() and by a
for loop.