Re: Data.Tuple impoverished

On Fri, 15 Jun 2012, Ivan Lazar Miljenovic wrote:

On 15 June 2012 17:59, Andreas Abel wrote:

...

Hi,

the module Data.Tuple offers a sad collection of 5 functions.  Many standard functions are missing.  For instance, I'd expect all the functions of

 Data.Tuple.HT  (package utility-th)

to be part of Data.Tuple, which are

 mapPair :: (a -> c, b -> d) -> (a, b) -> (c, d)  mapFst :: (a -> c) -> (a, b) -> (c, b)  mapSnd :: (b -> c) -> (a, b) -> (a, c)

I believe these are covered by Control.Arrow...

Yes, they are covered by 'first', 'second' and '***'. But I decided to implement them in Data.Tuple.HT because I think that the use of the pair type in 'first' and friends is not the focus of the arrow functions. It would be easy for me to add mapFst3, mapSnd3.

...

 -- swap :: (a, b) -> (b, a)  -- swap is present in Data.Tuple

I have also added such functions in order to allow people to write code that works for many different GHC and 'base' versions.

...

P.S.: I have reimplemented all these functions for myself, because I use them, but I am puzzled why they are not in the standard library.

You can import my package without having to regret. I promise not to add new dependencies and that it will remain Haskell 98.