fix(dummies): honour narrow-range exclusions with a type-aware nudge - #270
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When a draw collided with an excluded point, ContinuousIntervalSpec stepped with the static double-space NextUp instead of the type-aware _nextUp lambda. On Single and Half one double ulp above a representable value re-quantizes to the same value, so the walk stalled and a satisfiable specification exhausted the nudge budget and threw AnyGenerationException. AnyDouble was immune only because its quantize and nextUp are the identity. Step with the type-aware ladder and walk both directions: ascending first, then descending from the original draw when the ascending walk leaves the bounds, so an exclusion on either bound of a tight range is honoured. Check the next value against the bounds before clamping, so a genuinely exhausted range fails as a real "no value remains" condition rather than by budget exhaustion alone. Add regression tests per continuous type (Single, Half, Double) covering an exclusion inside a narrow range on either bound, a fully excluded range that must still throw a seeded AnyGenerationException, and seeded reproducibility. Refs: #207 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016wCNSRakgsbJXCVcVDNv87
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July 21, 2026 14:46
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Summary
On the narrow (quantized) floating-point generators (
AnySingle,AnyHalf), an exclusion inside a tight range made a satisfiable specification throwAnyGenerationExceptionfor a large fraction of seeds. The exclusion nudge inContinuousIntervalSpec.Generatestepped with the static double-spaceNextUpinstead of the type-aware_nextUpladder, so onedoubleulp above a representablefloat/Halfre-quantized to the same value and the walk stalled until the budget burned out. This fixes the nudge and makes it walk both directions.Type of change
Changes
ContinuousIntervalSpec.Generatenow nudges a colliding draw with the type-aware ladder (_nextUp) instead of the static double-spaceNextUp, so a step lands on the next representable value of the generator's own type.NudgeToFreehelper). An exclusion on either bound of a tight range is now honoured — previously only an exclusion below the drawn value could be resolved._min/_maxbefore clamping, so a genuinely exhausted range fails as a real "no representable value in range remains" condition rather than by budget exhaustion alone (the budget stays only as a backstop).Dummies.UnitTests/ContinuousExclusionNudgeTests.cs(6 tests).Testing
dotnet build FirstClassErrors.slndotnet test FirstClassErrors.slnFirstClassErrors.Analyzers.UnitTests)All test projects green on the rebased branch (
Dummies.UnitTests: 229). The new regression tests were also confirmed to fail without the source fix (4 of 6, with the pre-fix exception) and pass with it. Coverage per continuous type (AnySingle,AnyHalf,AnyDouble): an exclusion inside a narrow range on either bound, a fully excluded range that must still throw a seededAnyGenerationException, and seeded reproducibility.Documentation
doc/updateddoc/handwritten/for-users/README.fr.md) updated if user-facing behavior changedThe public contract is unchanged (
Except/DifferentFromnever yield the excluded value) — this only makes the engine honour it where it previously threw. No user-facing doc described the nudge, and the changed message is an internalInvalidOperationExceptiondetail referenced nowhere.Architecture decisions
Proposed: ADR-____The fix is an implementation detail of an internal engine; the "a satisfiable specification produces a value" contract already existed.
Related issues
Closes #207
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https://claude.ai/code/session_016wCNSRakgsbJXCVcVDNv87
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