RFC: Add HasCallStack constraint to partial Data.List functions.

[David Feuer]

On Fri, Jun 4, 2021, 12:12 PM Henrik Nilsson <
Henrik.Nilsson at nottingham.ac.uk> wrote:

> And besides those, there are other perfectly reasonable functions
> like (!!) and foldr1 that I'd definitely would not say never should
> be used, just as I would not say that array indexing or integer
> divisions must be shunned because they are partial.
>

FWIW, I think (!!) tends to show up an awful lot (maybe mostly) in code
written by beginners who aren't yet thinking of lists structurally. foldr1
is deceptive—it's easy to think it can do more than it can, and I've seen
its laziness characteristics confuse even an experienced Haskeller. It's
not even really nice for non-empty list types. Much clearer:

  fr1 :: (a -> b -> b) -> (a -> b) -> NonEmpty a -> b

which is best matched to

  data NonEmpty a = End a | Cons a (NonEmpty a)

but which can be adapted to Data.List.NonEmpty with a bit of laziness
muddling.

>
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