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nonEmptyTraverse for NEM with key mapping #4759

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nonEmptyTraverse for NEM with key mapping #4759

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12 changes: 12 additions & 0 deletions core/src/main/scala/cats/data/NonEmptyMapImpl.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -261,6 +261,18 @@ sealed class NonEmptyMapOps[K, A](private[data] val value: NonEmptyMap[K, A]) {
loop(head, tail).value
}

def nonEmptyTraverse[G[_], L, B](
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I think this name isn't right. Traverse on maps only uses the values, not the keys. So if you are going to use the keys I think we need a new name. Something like nonEmptyTraversePairs or traverseWithKey or something.

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NonEmptyMap already has map (values only) and mapBoth (keys with values). So I guess this should be nonEmptyTraverseBoth then.

f: (K, A) => G[(L, B)]
)(implicit G: Apply[G], ordL: Order[L]): G[NonEmptyMap[L, B]] = {
def loop(h: (K, A), t: SortedMap[K, A]): Eval[G[NonEmptyMap[L, B]]] =
if (t.isEmpty)
Eval.now(G.map(f.tupled(h))(b => NonEmptyMap(b, SortedMap.empty[L, B](ordL.toOrdering))))
else
G.map2Eval(f.tupled(h), Eval.defer(loop(t.head, t.tail)))((lb, acc) => NonEmptyMap(lb, acc.toSortedMap))
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Why wrap and unwrap with NonEmptyMap on every step? Why not do it once at the end after calling .value?


loop(head, tail).value
}

/**
* Typesafe stringification method.
*
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