Adding dup to Data.Tuple?

[Henrik Nilsson]

Hi,

Ivan Perez wrote:

 > The function \x -> (x,x) is very convenient when working with arrows.
 > Would it be appropriate to add it to Data.Tuple?

David Feuer replied:

 > I'm not opposed. Should this be called dup or diagonal? What about
 > larger tuples?

Dan Burton replied:

 > There is precedent in the arrow literature for calling this function
 > "dup"

It would indeed be unfortunate if it was not called "dup".

One could argue, as David (I'm guessing) does, that it's a bit of an
odd  definition to add to Data.Tuple as it only works for pairs
(as implied by its name).

And the reason it's convenient for Arrows is that (standard) Arrows
are defined in a way that relies on pairs.

So maybe it should somehow be defined in relation with Arrows.

But then again, all other functions in Data.Tuple are at present 
specific to pairs ("fst", "snd", "swap", ...).

So "dup" would certainly not look out of place there.


Best,

/Henrik





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