[Haskell-beginners] Re: Is this overkill?

[Zachary Turner]

On Fri, Apr 3, 2009 at 9:30 PM, Heinrich Apfelmus <apfelmus at quantentunnel.de
> wrote:

> Zachary Turner wrote:
> > I thought I would try to see if it were possible to write, in point-free
> > form using no lambda functions and no intermediate functions, a function
> > that takes 2 lists of Booleans, computes the pairwise logical AND of the
> two
> > lists, and returns a list containing the 0 based indices of the elements
> > where the logical and of the two was true.  I know that at some point it
> > becomes overkill and for the sake of readability one should know when to
> > draw the line.  So I want to see if someone with more experience than me
> can
> > comment on whether or not this is over the line :P
> >
> > trueIndices = curry $ map fst . filter snd . zip [0..] . map (uncurry
> (&&))
> > .. (uncurry zip)
> >
> > So do all the uncurries and curries make it too hard to understand or is
> it
> > pretty easy to read this?  For me it takes me a while to figure out by
> > looking at it because it's hard to trace all the currying and uncurrying.
> > And is there a more elegant solution?
>
> Looks very readable to me, though I'd write it as
>
>  trueIndices = (map fst . filter snd . zip [0..] .) . zipWith (&&)
>
> or even simply as
>
>  trueIndices xs ys =
>      map fst . filter snd . zip [0..] $ zipWith (&&) xs ys
>
> because composing functions with more than one argument tends to be a
> bit messy.
>
>
> With Conal's semantic editor combinators
>
>  http://conal.net/blog/posts/semantic-editor-combinators/
>
> it would be written as
>
>  trueIndices =
>    (result . result) (map fst . filter snd . zip [0..]) (zipWith (&&))
>


That was a pretty interesting blog post, and easily understandable which is
always nice.  Thanks for the link.  I also had never even used the zipWith
function, so thanks for pointing out that equivalence.
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