Spelling book solution for https://www.futurelearn.com/courses/functional-programming-haskell/4/steps/334999

speller.hs

-- | The 'wordPhrase' function spells out an individual word
-- For example, "a is for apple"
wordPhrase :: String -> String
wordPhrase x = (head x) : " is for " ++ x


-- | The 'speller' function generates text for a spelling book
-- from a list of words
speller :: [String] -> String
speller [] = []
speller [x] = wordPhrase x
speller [x,y] = xPhrase ++ ", and " ++ yPhrase
  where
    xPhrase = wordPhrase x
    yPhrase = wordPhrase y
speller (x:xs) = wordPhrase x ++ ", " ++ speller xs