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Title
j
Jannis
10/25/2019, 10:18 PMHey, in arrow the traverse method from the Traversable typeclass is usually (for collections) implemented using foldRight, but haskell's docs at http://hackage.haskell.org/package/base-4.12.0.0/docs/Data-Traversable.html state that travers is left to right. Is that a bug or a conscious decision? I am for changing that, because for infinite structures like sequence traverse would never compute anything and spend all its time forcing the sequence, whereas with a left to right manner it would actually compute stuff (and when used with IO can also abort whenever it wants)
This bad, albeit perfectly fine code will fail with traverse, but work just fine in haskell, that is due to lazyness. I believe this can be recreated using Eval and Option composed but that is very very ugly to do by hand, so maybe offer a short hand method?
Oh and ignore the custom applicative instance, I was writing this inside arrow-core-data where that does not exist, just ignore it mentally.
Also ignore what I said about maybe fixing this with eval, it can't be done, it needs to be fixed inside traverse.
Created an issue that contains a description of the (root) problem and an idea how to fix it. Any opinions?
https://github.com/arrow-kt/arrow/issues/1749
👏 1
s
simon.vergauwen
10/27/2019, 12:40 PMYes, I’ve noticed this before too
Thanks for the ticket and looking into it!