[Haskell-cafe] Haskell's "historical futurism" needs better writing, not better tools

David Feuer david.feuer at gmail.com
Thu Sep 16 22:51:42 UTC 2021

The last time I went to look at the laws it took me a couple minutes to
find them. I use them to write instances. Pretty important, IMO.

On Thu, Sep 16, 2021, 6:46 PM Viktor Dukhovni <ietf-dane at dukhovni.org>

> On Thu, Sep 16, 2021 at 04:57:28PM -0400, David Feuer wrote:
> > I am not a fan of how the new Traversable documentation buries the
> > actual laws.
> The laws are one click away from the table of contents, and IMHO not
> particularly illuminating other than for advanced readers.
> For example, in Data.Foldable they are:
>     foldr f z t = appEndo (foldMap (Endo . f) t ) z
>     foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z
>     fold = foldMap id
>     length = getSum . foldMap (Sum . const 1)
> is someone new to Data.Foldable really going to learn something from
> these before they've deeply understood the background concepts?
> My take is that the laws should almost always be "buried" (one click
> away) at the end of the module documentation.  Those who care and need
> them can find them, but I think they just intimidate the less
> experienced readers.  Putting the laws first likely only discourages
> beginners.
> --
>     Viktor.
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