Proposal: Add singleton function to Data.List module

[Sven Panne]

Am Do., 22. Aug. 2019 um 19:11 Uhr schrieb Kris Nuttycombe <
kris.nuttycombe at gmail.com>:

> On Thu, Aug 22, 2019 at 3:58 AM Sven Panne <svenpanne at gmail.com> wrote:
>
>>  I think there's a significant difference between "little helper" and
>> "the monomorphic function that is used to implement `pure`" - with a
>> slightly different framing, we might be able to come to an agreement that
>> both the monomorphic an polymorphic versions of this function are useful in
>> different contexts. [...]
>>
>
I think we can agree that we disagree here. ;-) My brain is too small to
remember the names of myriads of trivial helpers, so I very much prefer
general, orthogonal things. In our case: If we have a general, polymorphic
function (often from a type class), just use that. If for some reason
(rarely!) I want a more monomorphic function, I can just add a plain old
type signature somewhere (no need for funky language extensions like type
applications). This radically reduces the number of things one has to
remember. In our case: Know type classes + know a way to make things more
monomorphic.


> My guiding principle for API design is that one should always expose the
> fundamental building blocks as a low-level API, and then provide a smaller
> interface for the common use cases. Typeclass instances are no different -
> they are the general interface that allows us to invoke what is ultimately
> a monomorphic, low-level building block function in a polymorphic context.
>

This is exactly the opposite API design principle I have: Do not expose the
monomorphic functions if they are already in a type class. You can easily
reconstruct them as a library user via type signtures if this is really
needed (still haven't seen many convincing examples of that), but you can'
do it the other way round. Less things exposed, no generality/use cases
lost => easier to remember.

The thing we can probably agree on: API design is hard and it's not an
exact science, more a kind of art which is assessed in a subjective way...
:-)

>
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