Factor the suite's generators into a monad-polymorphic Generable class - #24
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Each shape the suite generates had a generator written specifically at `Plausible.Gen` (a `genXWith` per wrapper), even though the underlying `genX` combinators are already polymorphic in Basalt's `Gen`. Factor each into one interpretation-polymorphic `genXG`, add a `Generable` class naming the canonical generator per type, and derive every `Arbitrary` instance from it — calling `genXG` at `Plausible.Gen` with the existing `Gen.sized`/`retryGen` wrapping, so the draws are byte-for-byte unchanged and `lake test` behaves identically. Retry is now explicitly a per-interpretation harness concern rather than part of the generator: `genLExpr`'s `retryCont` (and the inner `retryGen` of the procedure/program generators) default to `id` in the canonical generator; the Plausible `Arbitrary` passes `retryGen`/`retryGenArg` on top. Covers all twelve wrapper types (expressions, commands, functions, statements, procedures, programs, ADT / independent blocks). Doc references to the removed `genXWith` helpers are updated. No new dependency beyond Basalt's `Gen` class and no behavior change to the Plausible suite; the registry's generators can now run under any `Gen` interpretation. Confirmed draw-for-draw identical to the original: because `Plausible.Gen` is a pure `StateT (ULift StdGen) (ReaderT (ULift Nat) (Except GenError))`, each `Arbitrary` can be run with an explicit `mkStdGen seed` and no global RNG. Dumping all twelve instances across a grid of seeds and sizes before and after the refactor produced byte-identical output (matching sha256).
ngernest
approved these changes
Sep 11, 2026
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The purpose of this change is to prepare for use of different
Basalt.Genbackends (including one backed by coverage-guided fuzzing), not justPlausible.Gen.Description of changes:
Each shape the suite generates had a generator written specifically at
Plausible.Gen(agenXWithper wrapper), even though the underlyinggenXcombinators are already polymorphic in Basalt'sGen. Factor each into one interpretation-polymorphicgenXG, add aGenerableclass naming the canonical generator per type, and derive everyArbitraryinstance from it — callinggenXGatPlausible.Genwith the existingGen.sized/retryGenwrapping, so the draws are byte-for-byte unchanged andlake testbehaves identically.Retry is now explicitly a per-interpretation harness concern rather than part of the generator:
genLExpr'sretryCont(and the innerretryGenof the procedure/program generators) default toidin the canonical generator; the PlausibleArbitrarypassesretryGen/retryGenArgon top.Covers all twelve wrapper types (expressions, commands, functions, statements, procedures, programs, ADT / independent blocks). Doc references to the removed
genXWithhelpers are updated. No new dependency beyond Basalt'sGenclass and no behavior change to the Plausible suite; the registry's generators can now run under anyGeninterpretation.Confirmed draw-for-draw identical to the original: because
Plausible.Genis a pureStateT (ULift StdGen) (ReaderT (ULift Nat) (Except GenError)), eachArbitrarycan be run with an explicitmkStdGen seedand no global RNG. Dumping all twelve instances across a grid of seeds and sizes before and after the refactor produced byte-identical output (matching sha256).By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.