steve-downey / transpose / 29591206305

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Committed by steve-downey

Commit Message

ap is a basis, invoke is the interface

Refinement of the pure/apply ruling (Steve, 2026-07-14): ap -- one-step
application of a callable-in-context -- is a perfectly cromulent basis
for Applicative and is supported as one: instances opt in with pure +
invoke or pure + ap, and the base derives the missing direction (the
currying cost confined to the derivation, never at call sites). ap also
remains available as a secondary operation exactly where the context
can hold a callable. What ap is not is the user-facing interface: the
verb papers, examples, and teaching lead with is the n-ary invoke, and
std::simd::vec (no vec<callable>) is the proof an ap-shaped interface
would lock out a motivating domain. The name is ap; apply stays gone.

The binary tree example returns to its role as the living ap-basis
exemplar (shape-aware pairwise recursion, invoke derived); optional/
zip_list/simd_lanes gain basis-coherence and secondary-ap tests; the
simd invoke-only pin stays and is the interface argument; D3200R0's
section is retitled 'ap as basis, invoke as interface' with proposed
operations and non-goals to match. 54/54 tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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