Adds the two canonical prefix-slicing combinators to std_list.
First fns in std_list to combine `if` + Int arithmetic + recursive
ADT pattern in one body.
take : forall a. (Int, List<a>) -> List<a>
— first n elements (or all of xs if shorter than n).
drop : forall a. (Int, List<a>) -> List<a>
— list with first n elements removed (Nil if n >= length).
Both use `(if (<= n 0) ...)` as the base-case guard since
literal sub-patterns inside Ctor patterns aren't yet supported
(queued as 16c — would let take/drop collapse the if into the
match).
examples/std_list_more_demo: builds [1, 2, 3, 4, 5] once and
exercises take/drop at n=0, n=mid, n=overflow on each. Expected
output 0, 3, 5, 5, 3, 0 (one per line).
Tests: 95/95 (e2e went from 35 to 36). std_list grew from 10 to
12 combinators; total stdlib 5 modules / 29 combinators. No new
compiler bug surfaced.
Pre-existing std_list defs are byte-identical (verified via diff
on .ailx and round-trip on .ail.json), so the five downstream
importers (std_list_demo, std_list_stress, std_either_list,
std_either_list_demo, list_map_poly) need no regeneration.
Second stdlib module. Tester wrote std_list.ailx (10 combinators,
164 LOC) and a consumer demo. std_list typechecked standalone;
demo did not, surfacing three compiler bugs:
1. Check-side: Iter 14h's qualify_local_types was applied to
Term::Var cross-module lookup but not to ctor-field types in
Term::Ctor synth or Pattern::Ctor resolution. First recursive
cross-module ADT (List has Cons a (List a) — recursive Con
self-ref) triggers the bug. std_maybe slipped through because
Maybe's ctors have no recursive Con field.
2. Codegen-side: same gap mirrored across 4 sites in codegen
(Term::Ctor synth, lower_ctor, lower_match) plus a tweak to
unify_for_subst (recurse on re-bind instead of strict equality
so sibling-derived List<Int> accepts nullary-ctor's List<$u>
wildcard).
3. Const codegen: emit_const rejected non-literal const bodies.
The demo's xs : List<Int> = Cons 1 (...) requires it. Fix:
per-module const table, Term::Var resolution loads literal
consts from global, inlines non-literal bodies. Bare and
qualified refs both supported.
All three fixes carry an "Iter 15b" code comment at their site.
~349/25 LOC across ailang-check, ailang-codegen, e2e.rs.
Tests 85 -> 87. New e2e std_list_demo asserts 11-line stdout:
length 5, is_empty false/true, head via from_maybe, tail length,
append length, reverse head, map double head, filter is_even
length, fold_left sum, fold_right sum. New ailang-check unit
test cross_module_recursive_adt_term_and_pat_ctor covers both
the original bug and the symmetric pat-ctor latent twin.
Hash invariance: all pre-15b fixtures + std_maybe defs
bit-identical. 14a / 14e / 14h regressions all green.
Cumulative state: 2 stdlib modules (std_maybe, std_list), 14
combinators, cross-module recursive ADT working end-to-end.
Three compiler bugs surfaced + fixed in dogfood since 14a (each
dogfood iter has surfaced ≥1).
Authoring observation: form (A) at 10 combinators is fine; main
friction is paren-counting in nested seq chains, not the form
itself. n-ary seq would help but is sugar.
Plan 15c: 1000-element list stress test for fold_left (tail-call-
marked) vs fold_right (constructor-blocked).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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