[Haskell-beginners] Non-exhaustive patterns

[Jim]

Hey guys,

Thiis is my function below:

notThe :: String -> Maybe String
notThe word
       | word /= "the" = Just word
       | word == [] = Just []
       | otherwise = Nothing

replaceThe :: String -> String
replaceThe word = go (words word)
       where go (x:xs)
               | notThe x == Just [] = []
               | notThe x == Just word = word ++ go xs
               | notThe word == Nothing = " a " ++ go xs


 > replaceThe "what"
"what*** Exception: chap12.hs:(13,13)-(16,55): Non-exhaustive patterns 
in function go

I thought I covered all the potential patterns in my replaceThe 
function. I'm not sure what pattern I've missed, any thoughts?

Best regards,

Jim