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Parameterize ADT tag types - #424
dathegreat wants to merge 1 commit into
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| Layer / File(s) | Summary |
|---|---|
Tag contracts and validation rel8-internal/src/Rel8/Internal/Type/Tag.hs, rel8-internal/src/Rel8/Internal/Generic/Table/ADT.hs, rel8-internal/src/Rel8/Internal/Generic/Table/ADT/Tag.hs |
ADTTag defines tag constraints and constructor mappings. Compile-time checks validate constructor counts, nullary tag constructors, and unique mappings. Helpers create and inspect tag columns. |
Tag-aware ADT serialization rel8-internal/src/Rel8/Internal/Generic/Table.hs, rel8-internal/src/Rel8/Internal/Generic/Table/ADT.hs |
Generic ADT columns and serialization now carry a tag type. Serialization and result conversion use tag values and tests. |
Tag-aware construction and deconstruction rel8-internal/src/Rel8/Internal/Generic/Construction.hs, rel8-internal/src/Rel8/Internal/Generic/Construction/ADT.hs |
Generic build, construction, deconstruction, and naming operations carry the tag type. Constructor matching uses tag-column expressions and tag mappings. |
Public API and default-tag integration rel8-internal/src/Rel8/Internal/Table/ADT.hs, rel8-internal/src/Rel8/Internal/Column/ADT.hs, rel8-internal/src/Rel8/Internal/Table/HKD.hs, rel8-internal/src/Rel8/Internal/Table/Rel8able.hs, rel8/src/Rel8.hs, rel8-internal/rel8-internal.cabal, changelog.d/20261022_000000_dmarcyes_adt_enum_tag.md |
Rel8 exports ADTWith, HADTWith, and the custom-tag APIs. Existing ADT APIs specialize to Tag. HKD and Rel8able integrations pass tag types through generic operations. |
Custom-tag test coverage rel8/tests/Rel8/ADTWith/Test.hs, rel8/tests/Main.hs, rel8/tests/type-errors/ADTTag.hs, rel8/rel8.cabal |
Tests cover enum-backed tags, constructor mappings, build and construction operations, nested ADTs, and compile-time validation failures. |
Estimated code review effort: 4 (Complex) | ~60 minutes
Sequence Diagram(s)
sequenceDiagram
participant Caller
participant buildADTWith
participant ggbuild
participant gmakeADT
participant gtagExpr
Caller->>buildADTWith: request constructor build
buildADTWith->>ggbuild: pass tag-indexed columns
ggbuild->>gmakeADT: pass constructor name and fields
gmakeADT->>gtagExpr: obtain constructor tag expression
gtagExpr-->>gmakeADT: return tag expression
gmakeADT-->>Caller: return tagged ADT expression
Suggested reviewers: chrisdone-artificial
Merge Risk: 
06625
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The custom-tag documentation concern is addressed. No remaining issue in the supplied review evidence prevents merge.
Pre-merge checks: 
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Check name Status Explanation Title check The title clearly and concisely describes the main change: parameterizing ADT tag types. Description check The description directly explains the new ADTWith and ADTTag functionality, generalized APIs, compatibility impact, motivation, and testing-related considerations. Docstring Coverage No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat… Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request. Full details: Docstring Coverage
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Explanation
No eligible functions found in the changed files. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 0 functions across 0 files. (1 skipped: 1 unsupported.)
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Finishing Touches
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Generate unit tests (beta)
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- Create a new PR
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- Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts
A rabbit checks each tag in place
Then hops through schemas at a pace
Enum leaves mark each constructor’s trail
Round trips return with every detail
The burrow’s types all match today
![coderabbitai[bot]](https://avatars.githubusercontent.com/in/347564?s=60&v=4){kind=small}
Hello maintainers! May I please get your thoughts on this feature before I spend time writing more haddock documentation for it? Are you interested in adding this functionality to Rel8?
Motivation
I ran into a scenario at my day job where I needed to encode an ADT in one of our tables. Because I generally prefer encoding database constraints at the type level if possible, I wanted to make the tag column a Postgres
enum, rather than atexttype. I also read #422 the other day, and thought this could be an interesting step in that direction as well (using something likeADTWith NoTag t, maybe?)AI Disclaimer
I used an LLM to assist with these changes. On a scale from vibe-code slop to 100% handwritten research paper, I would give this a 7/10.
Added
ADTWith tag ttype which generalizes theADTtype's hardcodedtexttag column, so the tag can be any type, such as a PostgreSQL
enum.ADTTagclass to define tag types. A tag type must be aNonNullDBTypewith
EqandDBEq, whose constructors are all nullary (zero parameters) andcorrespond one-to-one with the ADT's constructors. This tag <-> ADT bijection
is defined by
ADTTag's associatedTagConstructortype. Mismatches arereported as type errors.
...Withversions of the existing ADT types and functions, suchas
HADTWith,NameADTWith/nameADTWith,buildADTWithandconstructADTWith.Changed
ADT,HADT,ADTable,BuildableADT,ConstructableADT,NameADT, etc.are now synonyms for their
...Withversions applied toTag, such astype ADT = ADTWith Tag. Functions likebuildADTdelegate similarly totheir
...Withversions. Existing code using them is unaffected, apart fromthe following.
ADTis now a type synonym, instances on it such asinstance C (ADT t)requireFlexibleInstances. This is enabled by defaultin
GHC2021.