Haskell Foldable Wats

Nathan Bouscal nbouscal at gmail.com
Wed Feb 24 15:55:42 UTC 2016

On Wed, Feb 24, 2016 at 3:49 PM, Kosyrev Serge <_deepfire at feelingofgreen.ru>

> Nathan Bouscal <nbouscal at gmail.com> writes:
> > Apologies for being unclear. By marginal, I meant that I expect many
> > learners who end up confused by this would have otherwise come across
> > the same confusion by other paths.
> This sounds odd to me in two ways:
> 1. it is not "the same" confusion -- it is a worse confusion, for
>    several reasons:
>    - the questionable Functor instance gives a cognitive dissonance for
>      not transforming the entirety of the tuple (for good reasons, but
> still!)
>    - the questionable Functor is a puzzlingly arbitrary choice among a
>      N-family of options that an N-tuple provides.
As Ed pointed out, there is nothing arbitrary about the choice. This
actually makes tuples in some sense a uniquely good way of explaining how
things work, because you can show why this restriction exists.

> 2. but even if the confusion itself wasn't made worse -- its impact has
>    increased, because exposure to it has increased
To the extent that exposure has increased, I would think it would be caused
by confusion of the "lists vs tuples" type, which seems important to
resolve early. That resolution doesn't really need to say anything about
how Functor works, and can instead be more along the lines of "What problem
were you trying to solve by taking the length of a tuple? Should you have
been using a list instead?"

> --
> с уважениeм / respectfully,
> Косырев Сергей
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