[Haskell-beginners] Re: let indenting problems

[7stud]

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?