Real World Haskell, Ex. 3.2.6 (p.72 in Ja)

gistfile1.hs

import Data.List
sortByLength = sortBy ord
    where ord l1 l2 = if length l1 < length l2
                      then LT
                      else if length l1 > length l2
                      then GT
                      else EQ
        where l1l = length l1
              l2l = length l2
-- 8:8: parse error on input `where'

Why set l1l and l2l when you don't use them anyway?

A simple solution:

import Data.List

sortByLength ls = sortBy compare' ls
    where compare' l1 l2 = compare (length l1) (length l2)

Oh! It's so simple. Thank you.
But I want to know why the error occurred.

Indent the where line so that it starts further to the right than the line before:

                  else EQ
                     where l1l = length l1

Thank you very much.
Hmm, Offside rule is different for me.

http://en.wikibooks.org/wiki/Haskell/Indentation

I'll try to learn.