Haskell parse error in function definition

Question

I'm trying to compile this function:

fff [] _ = []
fff (x:xs) ys
   | r == [] = xs1
   | otherwise ys ++ xs1
   where r = filter (x<) ys 
         xs1 = fff xs ys

But I get this error:

Test.hs:14:4: parse error on input `where'

Failed, modules loaded: none.

Any help to solve it?

Thanks,
Sebastián.

Lee Duhem · Accepted Answer · 2014-04-23 02:36:04Z

2

You missed the required = after otherwise.

By the way, r == [] better be replaced by the more general null r.

Try this:

fff [] _ = []
fff (x:xs) ys
    | r == [] = xs1
    | otherwise = ys ++ xs1
    where r = filter (x<) ys 
          xs1 = fff xs ys

edited Apr 23, 2014 at 2:36

answered Apr 23, 2014 at 1:22

Lee Duhem

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1 Comment

bheklilr Over a year ago

The better reason to use null over == [] is because == [] requires that your list be of type Eq a => [a], where null :: [a] -> Bool, so null works on all lists, not just lists of Eq a => a values.

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