Functor, Applicative, Monad, Foldable, Traversable instances for (, , ) a b

Bryan Richter b at
Thu Mar 30 21:36:50 UTC 2017

On Thu, Mar 30, 2017 at 11:18:10PM +0200, Henning Thielemann wrote:
> On Thu, 30 Mar 2017, Bryan Richter wrote:
> >My intuition, based on observed usage in Haskell and elsewhere, is
> >that tuples are used as anonymous product types. Thus, I am
> >interested in the rationale for making them Functors because I feel
> >it has denied me a common, valuable tool. I no longer feel that I
> >should use pairs as product types. By making "(,) a" a Functor, it is
> >no longer an anonymous product type —— it is an anonymous Reader. Are
> >anonymous Readers really all that much more valuable than anonymous
> >product types? I cannot conceive it. I must be missing something.
> Pairs as functors are Writers. The function type got a Functor
> instance that corresponds to Readers.

Oops, laziness of the bad sort on my own part. :)

> I think the only reason is that some programmers got "laziness" wrong
> and try to use primitive types for everything instead of using (and
> importing) dedicated types.

Well, is there anything to be done for it at this point? Is there even
any consensus that this was, in retrospect, a poor choice?
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