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Mirror EchoAggregation: monoid fold, homomorphism law, no-canonical-disaggregation - #31
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…types#175) Finite-domain shadow of echo-types EchoAggregation.agda at 703dd77: Monoid, GroupAggregator, the fold and its homomorphism law (aggregation-as-fold), the sum/count/max/min instances, the generic no-canonical-disaggregation, and the macro Example-PairSum instance. Laws are checked on samples, never proved; the Agda stays the source of truth. avg is absent (not a monoid), as upstream. Adds 27 assertions (258 -> 285), including a negative control showing monoid_laws_hold can return false. No version bump; that is left to the owner. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV
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Merge Risk: 🔵 Low · up to
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| Check name | Status | Explanation |
|---|---|---|
| Title check |  |
The title clearly summarises the main change: adding the EchoAggregation mirror with monoid folds, homomorphism checks, and no-canonical-disaggregation checks. |
| Description check | |
The description directly explains the mirrored EchoAggregation API, its finite-sample scope, tests, and limitations. It is relevant to the changeset. |
| Docstring Coverage | |
No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0… |
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No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (3 skipped: 3 unsupported.)
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Review comments at @README.adoc:
- Around line 244-246: Update the README “Source of truth” paragraph to name
both the existing echo-types commit eed42503… and the EchoAggregation commit
703dd77, avoiding any conflicting provenance claim; also wrap the paragraph
around the EchoAggregation entry so line 246 matches the surrounding formatting.
Review comments at @src/EchoTypes.jl:
- Line 1339: Update the documentation for oplus_fold to state explicitly that it
performs a right fold/right association, matching its foldr implementation and
the Agda definition; leave the implementation unchanged.
- Around line 1398-1400: Update the first min_inf method so its second argument
is typed as Union{Nothing,Integer}, keeping the accepted domain closed and
consistent with the other overloads while preserving the existing
nothing/nothing result.
- Around line 1328-1332: Update monoid_laws_hold to materialise the input once
with collect, reject empty samples, and use the materialised collection for both
identity and associativity checks so one-shot iterators are handled correctly.
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🔇 Additional comments: 3
test/runtests.jl: 2
443-481: LGTM!
483-500: LGTM!README.adoc: 1
139-146: LGTM!
- monoid_laws_hold: materialise samples once (one-shot iterators work) and
reject an empty sample instead of returning a vacuous true.
- oplus_fold: document that it is a right fold, matching Agda's foldr.
- min_inf: type the nothing-first method's second argument as
Union{Nothing,Integer} so the domain is closed.
- README: name both provenance commits (eed4250 for the existing rows,
703dd77 for EchoAggregation); test count 285 -> 290.
Adds 5 assertions covering the one-shot iterator, the empty-sample error,
the closed min_inf domain and the right-fold direction.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV
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| `⊕-fold (xs ++ ys) == ⊕-fold xs ⊕ ⊕-fold ys`, checked at `xs`, `ys`. | ||
| """ | ||
| oplus_fold_append_holds(M::Monoid, xs, ys) = | ||
| oplus_fold(M, vcat(xs, ys)) == M.op(oplus_fold(M, xs), oplus_fold(M, ys)) |
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When xs and ys are non-array iterables such as generators, oplus_fold can consume their elements, but vcat(xs, ys) does not reliably perform iterator concatenation and may instead place the iterator objects in the combined collection, causing the monoid operation to receive generators and throw a MethodError. The same problem occurs in aggregation_as_fold_holds at line 1384; materialize each input once or use an iterator-concatenation operation before evaluating both sides.
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oplus_fold_append_holds and aggregation_as_fold_holds used vcat on their inputs. vcat of two generators nests them as elements instead of concatenating, so the former threw a MethodError and the latter returned a false counterexample on inputs that satisfy the law. Both now materialise their inputs once; oplus_fold does too, so one-shot iterables work. Adds 4 assertions (generator, filtered generator, aggregation over generators, fold of a filtered generator); 290 -> 294. Each failed before the change. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV
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| xs, ys = collect(xs), collect(ys) | ||
| oplus_fold(M, vcat(xs, ys)) == M.op(oplus_fold(M, xs), oplus_fold(M, ys)) |
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When xs and ys are multidimensional arrays, collect preserves their shape and vcat concatenates along the first dimension rather than appending their iteration sequences. For example, with the valid string-concatenation monoid, two 1×2 matrices are traversed as a,c,b,d after vcat, so this check returns false instead of comparing abcd on both sides; incompatible matrix shapes can throw instead. Although generator inputs are now materialized, this is fresh evidence that both this check and the analogous vcat in aggregation_as_fold_holds still need iterator-level concatenation or one-dimensional materialization.
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collect preserves array shape, and vcat of two matrices stacks rows instead of appending their iteration sequences, so with a non-commutative monoid (string concatenation) oplus_fold_append_holds returned false on inputs that satisfy the law. Inputs now go through a small _items helper (vec(collect(xs))), used by oplus_fold, oplus_fold_append_holds and aggregation_as_fold_holds. Arrays are read in column-major iteration order. Adds 3 assertions (294 -> 297); the append check failed before the change. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV
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| function oplus_fold_append_holds(M::Monoid, xs, ys) | ||
| # Materialise once: `vcat` of two generators would nest them as elements. | ||
| xs, ys = _items(xs), _items(ys) | ||
| oplus_fold(M, vcat(xs, ys)) == M.op(oplus_fold(M, xs), oplus_fold(M, ys)) |
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When xs and ys have different concrete element types, vcat promotes them to a common type before folding, so the combined side may receive converted values while the two separate folds receive the originals—for example, concatenating a large Int vector with a Float64 vector can round the integer. A valid type-sensitive monoid can therefore be falsely reported as violating the append law; the analogous vcat in aggregation_as_fold_holds has the same issue. This is fresh evidence beyond the prior iterator and array-shape fixes: the concatenation must preserve each original element rather than promote it.
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| pair_sum_is_fold(p::Tuple{Integer,Integer}) = | ||
| pair_sum(p) == oplus_fold(sum_monoid(), [p[1], p[2]]) |
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When p uses a narrower accepted Integer subtype, the direct sum and the fold can use different arithmetic because sum_monoid() fixes its identity as machine Int. For example, pair_sum_is_fold((Int8(100), Int8(100))) returns false: pair_sum performs overflowing Int8 addition, while the fold first combines the right operand with the Int zero and consequently computes 200 as an Int. Either restrict this API to Int or construct an identity compatible with the tuple's carrier so this advertised fold equality holds for every input accepted by the method.
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…nt-only (#32) ## Summary Follow-up to #31, which merged at 13:24:58Z on `9ef30be`, about 30 seconds before Codex finished reviewing that commit. Codex raised two P2 findings on it. Both reproduce, so this PR fixes them. ## Changes - **Type promotion in the fold-law checks.** `oplus_fold_append_holds` and `aggregation_as_fold_holds` joined their inputs with `vcat`, which converts element types. An `Int` next to a `Float64` is converted and can round. With an exact, non-promoting max (`Monoid(0, (a, b) -> a > b ? a : b)`) on `[2^53 + 1]` and `[Float64(2^53)]`, both checks returned `false` on a lawful monoid. They now use `_concat`, which keeps each element as given. - **`pair_sum` accepted any `Integer` tuple.** `sum_monoid`'s unit is an `Int`, so `Int8` inputs overflowed in the direct sum (`100 + 100 = -56`) but not in the fold (`200`), and `pair_sum_is_fold((Int8(100), Int8(100)))` returned `false`. The example models ℕ as non-negative `Int`, so `pair_sum` and `pair_sum_is_fold` are now restricted to `Tuple{Int,Int}`; other integer types raise a `MethodError` instead of silently disagreeing. ## Testing `julia --project=. -e 'using Pkg; Pkg.test()'` on Julia 1.10.4: **302 pass, 0 fail** (was 297). Both findings were reproduced before the change; the new assertions cover the promotion case for both checks and the `Int8` rejection. The README test count is updated to match. ## Notes - The commit is a cherry-pick of `dc1dd40`, which I pushed to the old `feat/echo-aggregation-mirror` branch after #31 had merged. That branch now exists on the remote again (it holds the merged history plus `dc1dd40`) and can be deleted. --- _Generated by [Claude Code](https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV)_ Co-authored-by: Claude <noreply@anthropic.com>
## Summary Prepares v0.4.0. No code change. - `Project.toml`: 0.3.0 → 0.4.0. - `CITATION.cff`: adds `version: 0.4.0` and `date-released: 2026-10-20`. - README and the source header no longer call `EchoAggregation` "unreleased". ## Why 0.4.0 and not 0.3.0 `Project.toml` already said 0.3.0, but the tags stop at `v0.2.0`: **v0.3.0 was never tagged**. Its content (the Tier-3 audience spine, 258 assertions) ships in v0.4.0 together with `EchoAggregation`, which is a new module. The README status paragraph says so. ## Readiness - `julia --project=. -e 'using Pkg; Pkg.test()'`: **302 pass, 0 fail**. - `main` at the #31 merge: Governance green; the Secret Scanner run was cancelled only because #32 landed a minute later. - This repository has no Julia CI job, so the test count is a local result, as it was for v0.1.0 and v0.2.0. - Stale and untouched: `.machine_readable/contractiles/Justfile` and `.machine_readable/6a2/PLAYBOOK.a2ml` still carry `0.1.0`. ## After merge The tag is the owner's to push (signed, annotated, admin bypass of the tag rule): ``` git tag -s -a v0.4.0 -m "EchoTypes.jl v0.4.0 — adds EchoAggregation" <merge-commit-sha> git push origin v0.4.0 ``` --- _Generated by [Claude Code](https://claude.ai/code/session_01MF5GeeBBDF6sUzr6pZTjWV)_ --------- Co-authored-by: Claude <noreply@anthropic.com>
Summary
Adds the executable finite-domain shadow of echo-types'
EchoAggregation.agda(general monoid/group aggregation, echo-types#175; mirrored from echo-typesmainat703dd77).What is mirrored
Monoid,GroupAggregator, the foldoplus_fold,aggregate_values.oplus_fold_append_holdsandaggregation_as_fold_holds.sum_monoid,count_monoid,max_monoid,min_monoid(nothing= ∞), pluscount_aggregator.no_canonical_disaggregation_of(=no_section_of_collapsing_mapunder aggregation names, as upstream).Example-PairSum:pair_sum,pair_sum_is_fold,pair_sum_collapses,pair_sum_non_injective,no_canonical_disaggregation_pair_sum.Honest scope
assoc, the identities and the fold law for all inputs; Julia checks them on supplied samples, so every*_holdsis a falsifier on its data.avgis absent because it is not a monoid, as upstream.Testing
julia --project=. -e 'using Pkg; Pkg.test()'on Julia 1.10.4: 285 pass, 0 fail (was 258; +27 across two new testsets). Includes a negative control (Monoid(0, -)is rejected bymonoid_laws_hold) and a matched negative (an injective map does not fire the no-section witness).Notes for the owner
CITATION.cffchange; the README marks this "unreleased on top of v0.3.0".Generated by Claude Code