Traversing infinite sequences

From @mausch on April 16, 2014 21:23

Traversing an infinite list works fine in Haskell: http://ideone.com/GuytMd But the equivalent F# + FSharpPlus code doesn’t terminate and eats infinite memory:

let x = traverse (fun x -> if x > 4 then Some x else None) (Seq.initInfinite id)

This is probably because foldr is currently strict for seq

Maybe a specialized foldr would work here, e.g. http://fpish.net/blog/anton.tayanovskyy/id/1453/http~3a~2f~2fwww.intellifactory.com~2fblogs~2fanton.tayanovskyy~2f2009~2f12~2f11~2fFoldr-or-FoldBack-on-Infinite-F~21sharp~21-Sequences.article

(BTW this stackoverflow question made me realize this).

Copied from original issue: gmpl/FsControl#26

[gusty]

#268 solves this issue in a generic way

It requires to have available a predicate (as part of the applicative abstractions) which tells whether an element is the cancelling element for the operation, called left-zero.

[gusty]

Here you can get an idea of how the unified function would look like