I'm learning 'Either' data structures in Haskell and have written the following:

```
type PhoneBook = [(String, String)] 
createPhoneBook :: PhoneBook --Use function to generate instance of type
createPhoneBook = [("betty","1212-232"),
                   ("billy", "3443-434"),
                   ("derdre", "3232-221")]

data PresentInPhoneBook = Present | NotPresent deriving (Show, Eq) --Either 
type IsPresent = String
type IsNotPresent = String

checkPhoneBook :: String -> PhoneBook -> Either IsPresent IsNotPresent
checkPhoneBook name pb = if foldRes == True then Left "Match" else Right "No Match"
where 
    foldRes = foldl (\acc (key,value) -> if key == name then True else acc) False pb

```

Are there any improvements to make this code more readable? 

I appreciate its a trivial example, but I'm just learning at this stage.