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Optimize Apply methods in FlatMap #2597

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merged 4 commits into from
Nov 9, 2018
Merged

Optimize Apply methods in FlatMap #2597

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37ad1f0
optimize productL/R in FlatMap
kailuowang Nov 5, 2018
f3cfcd4
slightly optimized ap2 and map2 as well
kailuowang Nov 5, 2018
aab72a8
reorg
kailuowang Nov 5, 2018
0a9f9d9
fmt
kailuowang Nov 5, 2018
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12 changes: 12 additions & 0 deletions core/src/main/scala/cats/FlatMap.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,18 @@ import simulacrum.noop
override def product[A, B](fa: F[A], fb: F[B]): F[(A, B)] =
flatMap(fa)(a => map(fb)(b => (a, b)))

override def ap2[A, B, Z](ff: F[(A, B) => Z])(fa: F[A], fb: F[B]): F[Z] =
flatMap(fa)(a => flatMap(fb)(b => map(ff)(_(a, b))))

override def map2[A, B, Z](fa: F[A], fb: F[B])(f: (A, B) => Z): F[Z] =
flatMap(fa)(a => map(fb)(b => f(a, b)))

override def productR[A, B](fa: F[A])(fb: F[B]): F[B] =
flatMap(fa)(_ => fb)
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Coming back to this, the lack of symmetry between productR and productL feels a little off to me. I think that the override of map2 makes sense. But maybe productL and productR should both just delegate to map2?

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Unlike productL, productR using map2 will incur one extra map. That's where the asymmetry comes from.

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Oh right. Sorry that I've required so much explanation on this one 😬

LGTM. @mpilquist does this PR look good to you?

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Yep looks good to me


override def productL[A, B](fa: F[A])(fb: F[B]): F[A] =
map2(fa, fb)((a, _) => a)

/**
* Pair `A` with the result of function application.
*
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