[Haskell-beginners] Beginners issue with 'Why Haskell matters' example code

Patrick Lynch kmandpjlynch at verizon.net
Thu Mar 10 15:32:39 CET 2011

Good morning,
Take a look at the following - it comes from Graham Hutton's book: "Programming in Haskell" - see link: http://horna.org.ua/books/fp-papers/Hutton,%20Graham%20-%20Programming%20in%20Haskell.pdf

qsort :: (Ord a) => [a] -> [a]
qsort [] = []
qsort (x:xs) = qsort smaller ++ [x] ++ qsort larger
                   smaller = [a|a<-xs, a <= x] 
                   larger   = [a|a<-xs, a >   x] 

----- Original Message ----- 
  From: Michael Anckaert 
  To: beginners at haskell.org 
  Sent: Thursday, March 10, 2011 2:46 AM
  Subject: [Haskell-beginners] Beginners issue with 'Why Haskell matters' example code

  Hey everyone

  I'm new on the list here and just started out learning Haskell and functional programming. I have over 12 years experience programming in various languages, from C to Python. 

  I started out with the Why Haskell matters paper (http://haskell.org/haskellwiki/Why_Haskell_Matters) and ran into a problem with the code below. It's discussed in the paper but when I save it to test.hs and load it into ghci, I get the following output:

  [1 of 1] Compiling Main             ( test.hs, interpreted )

  test.hs:6:22: parse error on input `='
  Failed, modules loaded: none.


  Could someone give a pointer on where my error lies?

  qsort [] = []
  qsort (x:xs) = qsort less ++ [x] ++ qsort more
      where less = filter (<x) xs
          more = filter (>=x) xs

  Kind regards
  Michael Anckaert <michael.anckaert at sinax.be>


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