Spelling book generator

spelling.hs

speller :: [[Char]] -> [Char]
speller list =
  spell (filter ((/=) "") list)

spell :: [[Char]] -> [Char]
spell [] = []
spell [single] = 
  isFor single
spell [first, second] = 
  isFor first ++ " and " ++ isFor second
spell (first:rest) = 
  isFor first ++ ", " ++ spell rest

isFor :: [Char] -> [Char]
isFor [single] =
  single : " is just " ++ [single]
isFor (first:rest) = 
  first : " is for " ++ (first:rest)