Add/fix Foldable extensions: findM and collectFirstSomeM #2421
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## master #2421 +/- ##
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+ Coverage 95.2% 95.22% +0.01%
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Lines 6366 6371 +5
Branches 280 279 -1
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| def findM[G[_]](p: A => G[Boolean])(implicit F: Foldable[F], G: Monad[G]): G[Option[A]] = | ||
| F.foldRight(fa, Eval.now(G.pure(Option.empty[A])))((a, lb) => | ||
| Eval.now(G.flatMap(p(a))(if (_) G.pure(Some(a)) else lb.value)) | ||
| ).value |
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I’m worried about stack safety here. Note findM, foldM and existsM use tailRecM to be stack safe.
Can we make Source package private so that we can use it here with tailRecM?
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Good point. I assumed stack-safety is provided by safe flatMap implementation. Will rework via tailRecM.
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Also added stack-safety tests for other monadic folds.
Fix implementation for findM and collectFirstSomeM extensions for Foldable vai tailRecM, make Foldable.Source package private
catostrophe
changed the title
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Can anything else be improved here to give it the green light? |
| * }}} | ||
| */ | ||
| def findM[G[_]](p: A => G[Boolean])(implicit F: Foldable[F], G: Monad[G]): G[Option[A]] = | ||
| G.tailRecM(Foldable.Source.fromFoldable(fa))(_.uncons match { |
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couldn't this be collectFirstSome { a => p(a).map(if (_) Some(a) else None) }?
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Sure it could but would require an extra map for each iteration. I just followed the recommendation of other contributors to prefer efficiency over conciseness in code.
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Shall we merge this, then? :) |
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@catostrophe Thanks for cleaning up after me |
#2365 seems abandoned, so this is a rework of
findMimplemented as a syntax extension for binary compatibility. Another but equivalent implementation chosen, becauseFoldable.Sourceis private.