+1. Use of tuples is highly discourageable, except for returning multiple arguments from a function. For everything else, roll your own datatype, to give the reader of your code some semantics, and to introduce more redundancy to avoid erros. I see no point in Functor or Foldable for tuples. I also do not see why (a,a) could not be a container of exactly two elements, as opposed to current GHC which insists it is a container of exactly one element. (Case for the mental institution, I'd say.) Cheers, Andreas On 18.02.2016 14:04, Henrik Nilsson wrote:
Hi,
On 02/18/2016 12:41 PM, Manuel Gómez wrote:
And whenever I have wanted to map on tuple fields (which I do from time to time), I most certainly want the ability to map on any field. Anyone with a couple of decades of Haskell experience ought to understand that the desire to map on any field of a record cannot be served by a typeclass such as Functor.
Yes, that's exactly my point: functor is not the right tool. So why make tuples instances of functor in the first place?
And yes, there is arguably an asymmetry of sorts in having to pick an order among type constructor arguments. But that does not change the fact that there is symmetry in having a projection function for each field. So why even entertain a notion of mapping that doesn't grant the same privileges to all fields?
Might be useful in some specialist applications, but certainly not what I, at least, would consider particularly useful.
Best,
/Henrik
-- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel@gu.se http://www2.tcs.ifi.lmu.de/~abel/