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...

 -- swap :: (a, b) -> (b, a)  -- swap is present in Data.Tuple  forcePair :: (a, b) -> (a, b)  fst3 :: (a, b, c) -> a  snd3 :: (a, b, c) -> b  thd3 :: (a, b, c) -> c  curry3 :: ((a, b, c) -> d) -> a -> b -> c -> d  uncurry3 :: (a -> b -> c -> d) -> (a, b, c) -> d

I wouldn't mind seeing these though.

Is there a good reason why they aren't?

Cheers, Andreas

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.

-- Andreas Abel  <><      Du bist der geliebte Mensch.

Theoretical Computer Science, University of Munich Oettingenstr. 67, D-80538 Munich, GERMANY

andreas.abel@ifi.lmu.de http://www2.tcs.ifi.lmu.de/~abel/

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On 15/06/12 09:59, 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, ... Is there a good reason why they aren't?

I am strongly in favor of adding these functions to Data.Tuple, there is no good reason for them not to be there. I would also support in addition to mapTriple, mapFst3, etc. Twan

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

These three could be replaced by a more general (and often defined) bifunctor class class Bifunctor f where bimap :: (a -> c) -> (b -> d) -> f a b -> f c d mapFst :: (a -> c) -> f a b -> f c b -- or mapL mapSnd :: (b -> d) -> f a b -> f a d -- or mapR This class also has a useful instance for Either in Base.

fst3 :: (a, b, c) -> a snd3 :: (a, b, c) -> b thd3 :: (a, b, c) -> c

This naming scheme for extractors from pairs (then triples) doesn't really extend to 4 tuples or higher, maybe a rethink is useful before a commit to the Base libraries. Of the top of my head, fst and snd are the only bits of "vowel dropping" as a naming scheme I can think of in Base, maybe it is not a tradition to continue, though SML has a few more like hd and tl.