Question

when trying to define a function that would remove the largest subset of set m that is also a subset of set a from set a, I encountered the following error:

filename.hs:7:33:parse error (possibly incorrect indentation)

for the following code:

exclude :: Integral t => [t] -> [t] -> [t]
a `exclude` m
           | m == [] = a
           | a == (b ++ c) = b
           | otherwise = []
           where b /= []
           where c = [z | z <- m]

how do I implement multiple conditions/definitions (using where or otherwise), or correct the function to properly work in a different way?

Answer 1

Saying “the largest subset of set m that is also a subset of set a”
is the same as saying “all elements of m that are also elements of a“.

Then the solution to your problem is stated simply as:

exclude a = filter (`notElem` a)

which when applied to m will give you a subset of m modulo any elements
that are also members of a. That is, it will “remove the largest subset of
m that is also a subset of a“.