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From: Paul Rubin <no.email@nospam.invalid>
Newsgroups: comp.lang.forth
Subject: Re: :Re: My LOOP is ugly
Date: Tue, 29 Nov 2016 23:31:10 -0800
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Xref: csiph.com comp.lang.forth:52980

Melzzzzz <mel@zzzzz.com> writes:
> Haskell:
> ....
> p2b = let f :: [(a,b)] -> (a,[b])
>           f x = foldl (\(a,b) (_,y) -> (a,y:b)) (fst.head $ x,[snd.head $ x]) (tail x)
>           in map (\x->(fst $ f x,sort.snd $ f x))
>             . groupBy (\x y-> fst x == fst y ) . sort 
> ...

{-# LANGUAGE TransformListComp #-}
import GHC.Exts (sortWith, groupWith, the)
import Data.Char (toUpper)
import Data.Function (on)

p2b xs = [ (the a, b) | (a,b) <- xs
         , then sortWith by b
         , then group by a using groupWith 
         ]

t1 = [('C',3),('A',1),('B',2),('A',2),('C',2)]
t2 = [("bar",44),("Foo",2),("foo",22),("BAR",4)]

main = do
  print . p2b $ t1
  print . p2b $ [(map toUpper a, b) | (a,b) <- t2]

================================================================

*Main Prelude> main
[('A',[1,2]),('B',[2]),('C',[2,3])]
[("BAR",[4,44]),("FOO",[2,22])]