Proposal: Add foldrWithIndex and foldlWithIndex to Data.List

[Ganesh Sittampalam]

I see, thanks. Could this be done via a rewrite rule from that idiom to
an internal implementation function instead?

On 22/10/2014 20:19, David Feuer wrote:
> Yes, they do. In particular, the zip can only fuse with one of the two
> lists so the Ints could be unboxed, or fusion optimizations could happen
> with the list folded over, but not both. The fold_WithIndex function can
> manage both at once. That said, I think there have been some pretty good
> arguments against adding these, or at least against adding them with
> these names.
> 
> On Oct 22, 2014 3:13 PM, "Ganesh Sittampalam" <ganesh at earth.li
> <mailto:ganesh at earth.li>> wrote:
> 
>     On 16/10/2014 18:14, David Feuer wrote:
> 
>         These functions can be lifted pretty much straight out of
>         Data.Sequence.
>         In particular, foldrWithIndex makes for a particularly nice
>         expression
>         of a fusing findIndices function, as is present in Data.Sequence.
> 
> 
>     Do these do anything better than just adding indicies first with the
>     standard zip [0..] idiom?
> 
>     Cheers,
> 
>     Ganesh
> 
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