feature: mapr off tree-bridge (Phase 2 PR3b, partial)#389
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Phase 2 PR3b starts the HOF finalizer migration. mapr 2 previously round-tripped every per-element callback through the tree-bridge (OP_CALL_BUILTIN_TREE), paying a NanVal-to-Value cost per call and depending on the ACTIVE_AST_PROGRAM TLS being live. Now mapr emits its own foreach loop using OP_CALL_DYN per element, with an ISERR check that short-circuits on first Err (out_reg = res and skip the wrap-acc tail), an ISOK typecheck that panics with a mapr-shaped message on a non-Result callback, an OP_UNWRAP of the Ok inner before appending to the acc list, and a final OP_WRAPOK to assemble Ok(L T) on the natural exit. No new opcode is needed since OP_WRAPOK already exists; that's why mapr ships in PR3b ahead of srt/grp/uniqby which all need dedicated finalizer opcodes. The closure-aware OP_CALL_DYN from the Phase 2 PR1/PR2 work means capturing lambdas work here without any further plumbing. The mapr! and mapr!! auto-unwrap forms are handled by emit_result_unwrap on the final out_reg, matching the bridge's behaviour exactly. The remaining HOFs needing finalizer opcodes (srt 2, grp 2, uniqby 2) are deferred to PR3c.
Seven cases across tree, VM, and Cranelift: - non-capturing inline lambda - capturing inline lambda (single capture, multiplier) - named fn-ref - empty input (vacuous Ok empty list) - short-circuit on first Err mid-list - all-Ok run with the same short-circuit-capable predicate - short-circuit on the very first element (acc-empty edge) Plus an examples/mapr-shortcircuit.ilo with -- run / -- out assertions so tests/examples_engines.rs exercises the lift across every engine. The example also serves as in-context learning for agents reaching for mapr in future.
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This was referenced May 18, 2026
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Phase 2 PR3c completes the HOF native dispatch migration. The 2-arg
forms of srt, grp, and uniqby previously round-tripped every per-
element callback through the tree-bridge (OP_CALL_BUILTIN_TREE),
paying a NanVal-to-Value cost per call and depending on the
ACTIVE_AST_PROGRAM TLS being live.
Each now emits its own foreach loop using OP_CALL_DYN per element to
fill two parallel scratch lists (keys + values), then hands them to a
dedicated finalizer opcode:
OP_SRT_BY_KEY (179) — sort vals by key; mixed-type-key fallback
folds to Ordering::Equal, matching the tree
walker exactly.
OP_GRP_BY_KEY (180) — bucket vals into a Map<MapKey, List<value>>;
numeric keys floor to i64; non-finite numbers
and non-t/n/b keys raise a typed runtime err.
OP_UNIQ_BY_KEY (181) — dedup using HashSet<String> with type-prefixed
keys (t:/n:/b:) so values from disjoint
domains never alias, matching the tree
scheme.
Each finalizer ships a free fn that the VM dispatch arm and Cranelift
JIT/AOT helpers share, so the two paths can't drift. The closure-
aware OP_CALL_DYN from Phase 2 PR1/PR2 means capturing lambdas work
here without further plumbing.
A single emit_hof_keyed_finalize helper covers all three HOFs at the
compiler layer; the only per-HOF variation is which finalizer opcode
to emit.
mapr already shipped its native lift in PR3b (#389), so this completes
the Phase 2 HOF migration that started with partition in PR3 (#387).
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Summary
Phase 2 PR3 (#387) lifted
partition 2off the tree-bridge. This PR extends the migration tomapr 2, the smallest of the four remaining bridge HOFs and the only one that needs no new finalizer opcode (a single existingOP_WRAPOKfinishes the assembly step).The original PR3b scope was all four remaining HOFs (
srt 2,grp 2,uniqby 2,mapr 2). After investigating the surface area (per-HOF new opcode 179-182 + VM dispatch arm + Cranelift JIT helper + AOT helper + tree-bridge eligibility removal + 4-5 cross-engine tests + example, multiplied by four) I time-boxed to the one that was tractable end-to-end with cross-engine parity. The other three are deferred to PR3c with a clear pattern to follow — see below.Manifesto framing:
mapris reached for by agents doing Result-aware data validation pipelines. The bridge round-trip paid a NanVal-to-Value cost per element and pinned the run to a live ACTIVE_AST_PROGRAM TLS. The native lift removes both and aligns mapr with the other native HOFs (map,flt,fld,flatmap,partition).Repro before/after
Before this PR the VM/Cranelift paths re-entered the tree interpreter for each callback. After this PR all three engines run the same
OP_FOREACHPREP/NEXT+OP_CALL_DYN+OP_ISERR/OP_ISOK+OP_UNWRAP+OP_LISTAPPEND+OP_WRAPOKbytecode shape. Output is byte-identical across tree, VM, and Cranelift JIT.What's in the diff
vm: lift mapr 2 off tree-bridge with ISERR short-circuit — new arm in
RegCompiler::compile_exprthat emits the native bytecode shape directly, mirroringpartition 2from feature: HOF native closure dispatch (Phase 2 PR3) #387 plus the short-circuit pattern and theOP_WRAPOKfinalizer.Mapr 2removed fromis_tree_bridge_eligible. Themapr!/mapr!!unwrap forms are handled byemit_result_unwrapon the produced Result, matching the bridge's behaviour. Non-Result callback returns raise throughOP_PANIC_UNWRAPwith a "mapr: fn must return a Result" message that contains the same substrings the tree-walker raises.test: cross-engine coverage for mapr native dispatch —
tests/regression_phase2_hof_finalizers.rswith 7 cases covering non-capturing lambda, capturing lambda, named fn-ref, empty input, short-circuit mid-list, all-Ok run, and short-circuit on the very first element (acc-empty edge). Each case runs on tree / VM / Cranelift JIT. Plusexamples/mapr-shortcircuit.iloso the example harness exercises the lift cross-engine too.Test plan
cargo test --release --features cranelift— full suite green (3180 + the rest)cargo fmt --checkcleancargo clippy --features cranelift --release --tests -- -D warningscleanexamples/mapr-shortcircuit.iloand runs it across every engineFollow-ups (PR3c)
The remaining bridge HOFs that need dedicated finalizer opcodes are deferred to PR3c:
srt 2 fn xs— needsOP_SRT_BY_KEY(slot 179): collect(key, value)pairs via OP_CALL_DYN per element, finalizer sorts in-place with Number/Text/mixed key handling matching the tree-walker.grp 2 fn xs— needsOP_GRP_BY_KEY(slot 180): finalizer buildsMap<MapKey, Vec<value>>using the existingMapKey::Int(n.floor() as i64)for finite numbers + Text fallback for Bool.uniqby 2 fn xs— needsOP_UNIQ_BY_KEY(slot 181): finalizer walks aHashSet<String>with the existing type-prefixed key scheme (n:/t:/b:) and appends only first occurrences. Matches tree-walker semantics exactly; no new MapKey path.Each needs a per-HOF extern "C" Cranelift helper mirroring the partition #387 pattern (
helpers.srt_by_keyetc), plus AOT wiring incompile_cranelift.rs, plus tree-bridge removal. Pattern is established by this PR.No doc update needed
This is a behaviour-restoration lift — the
maprsignature, return type, and semantics are unchanged. SPEC.md / ai.txt / SKILL.md / docs/reference/builtins.md already covermapr fn xs : R (L T) e. Internal refactor only.