Reviewing flatiron's morsel batching for applicability turned up something
better hiding under the lazy machinery: every cell over a concrete
collection was produced by slicing the REMAINDER ((tuple/slice c 1) per
element in coll->cells, and rest/next sliced the same way), so any full walk
was O(n^2). mapv over 40k elements took 10.4 SECONDS; a 20k-element
first/rest loop took two.
Cells over indexed collections now walk by INDEX (one shared indexed-cells
helper, O(1) per step), and rest/next of a vector/tuple/list return an O(1)
lazy view from index 1 — which also makes (rest [1 2 3]) a SEQ, as in
Clojure (it was a vector-typed slice; seq?/vector? rows pin the change).
mapv 40k: 10405 -> 182 ms. rest-loop 20k: 2040 -> 31 ms. Whole bench:
seq-pipe -28%, into-vec -24%, str-join -18%, hof -26%, TOTAL 4565 -> 3753
(-18% vs main, back to back). Chunked seqs (jolt-yqc) drop in priority:
the quadratic walks were the actual cost; chunking now only amortizes
per-element closure allocation.
Nine regression rows incl. 20k/50k linear-scaling smoke tests. Gate exit 0.
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