Filter letters from string replacing symbols for blanks spaces and letters lowercase

Question

Example: "Paul's! Come There"

GetOutput: "paul s come there"

 myFilter :: String -> String
 myFilter str = unwords . filter (not . null) . map (
                              map toLower . filter  isLetter
                              ) . words $ str

How can I filter the letters into lowerCase and at the same time replace all non-word symbols with blanks?

Answer 1

@Cirdec That's the idea. To get the syntax correct that would be map (\\c -> if not (isLetter c) then ' ' else c) (note the parenthesis) which is the same as map (\\c -> if isLetter c then c else ' ')