The roadmap's capstone: now that two folds exist (render, execute), extract the machinery
they share. host/comp-fold (compose.sx) is the reusable core — the seq/alt/each combinator
dispatch + the `when` predicate set (host/comp--pred?) + the context-environment + the `each`
source (host/comp--source) + recursion + the depth guard, ALL in one place. A domain plugs in
via a small dict {:empty :combine :leaf :overflow}; only its leaves and how results combine
differ:
render = {:empty "" :combine str …} leaf -> markup (+ row/grid layout combinators)
execute = {:empty (list) :combine concat …} leaf -> effect
host/comp-render and host/exec-run are now one-liners over host/comp-fold with their domain.
execute.sx shed its own seq/alt/each dispatch — it's just a dict + a leaf. A THIRD domain
(eval/reduce/extent over the same algebra) is now only a new dict + leaf, no new control flow.
Both folds went through the core with ZERO behaviour change: new tests/compose.sx exercises
the core + render domain directly (17/17 — leaves, seq, row, alt+when (has/eq/not), each
(items/query/empty), tmpl recursion over a (children) tree + depth guard, ref transclude, one
object two contexts); execute 13/13; blog 162/164 (2 pre-existing relate-picker fails). Full
host conformance 388/390. Wired tests/compose.sx into conformance.
plans/composition-objects.md roadmap steps 1-8 COMPLETE.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
The keystone validation of the universal-algebra thesis. lib/host/execute.sx is a SECOND
interpreter over the SAME seq/alt/each composition algebra as the render-fold — but a
different fold: leaves are EFFECTS, seq = steps in order, alt+when = branch, each =
for-each, and the accumulator is an effect log instead of an HTML string. It REUSES
compose.sx's shared machinery verbatim — host/comp--pred? (when), host/comp--field
(field/value), host/comp--source (each source) — so the predicate set, context-environment,
and iteration source are domain-agnostic; only the leaf semantics + accumulator are new.
KEYSTONE (tested): ONE (alt (when (has "auth") …) …) skeleton + ONE context folds two ways
— render picks the branch → "<b>in</b>", execute picks the SAME branch → {:verb "enter"}.
A publish workflow (validate → branch-on-status → notify-each) runs as one execute-fold over
a composition object. So the behaviour model (Slice 9) is "an execute-fold over a composition
object", not a separate system — the way the recursive tree proved recursion, this proves the
algebra is domain-agnostic. host/exec-run; 13/13 (new execute suite); wired into conformance
+ serve. Full host conformance 371/373 in 42s (warm); the 2 fails are the pre-existing
relate-picker pair.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
