[Haskell-beginners] Re: let indenting problems

7stud bbxx789_05ss at yahoo.com
Mon Mar 2 15:08:19 EST 2009

Heinrich Apfelmus <apfelmus <at> quantentunnel.de> writes:
> How about
>    import Data.Ord (comparing)
>    mySort = sortBy (comparing length)

I just finished chap. 3 of Real World Haskell, which doesn't 
even imports.  It took me hours to figure out how to 
access sortBy.  The book hasn't introduced "comparing", yet.

> or at least
>    mySort = sortBy myCompare
>        where
>        myCompare x y = compare (length x) (length y)

Very nice.  The book mentioned the compare function in 
chap. 2.  

I have a question about that code: how come you
don't have to specify a parameter for mySort, for example:

mySort xs = ...

And doesn't sortBy require two arguments?

sortBy :: (a -> a -> Ordering) -> [a] -> [a]
                 (1)              (2)

How come you can write it with only one argument?

Finally, l'm wondering if anyone can explain why my
let examples failed?

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