I've got one of those algorithms which "threatens to march off the right edge" (in the words of Goerzen et al). I need something like a State or Maybe monad, but this is inside the IO monad. So I presume I need StateT or MaybeT. However, I'm still (slowly) learning about monads from first principles. I thought I might present my code and get some pointers... maybe someone could actually show me how to rewrite it, which would be a neat way to see MaybeT and StateT in action. I'm hoping to get anything from a one-line response to a rewrite of my code. Anything will help. Here's the program: {- This is a program which starts with a document containing "notes" about software requirements (in a particular format) and puts them into a database. Notes include details such as the "source" of the requirement (who gave it), the topic(s) to which it pertains, the date, etc. I have written a parser to take a text document typed up by me during a meeting and parse it into a NoteRecord structure. Here is the structure: -} data NoteRecord = NoteRecord { recordSource :: String, -- Name of person who gave req. recordDate :: [Int], -- Date in [<year>,<month>,<date>] recordSourceType :: String, -- "meeting", "phone", "email", etc. recordBugNum :: Maybe Int, -- Bugzilla # (if relevant) recordTopics :: [String], -- list of official topics pertaining recordText :: String } -- the text of the note itself deriving (Show) {- One other wrinkle. The source (person name) and topic must be one of a set of pre-determined strings. A person has an official full name which is stored in the database. Topics also have official descriptive strings. If I wasn't clever, then the note, as I type it up, must have the exact name and topic. But I hate trying to remember things like that. So I have implemented a "fuzzy string match" system so that I can type part of someone's name (or even misspell it) or part of a topic string, and the system will find the best match to an official string. In pseudocode, the function to insert a note in the database must do this: This function starts with a NoteRecord. - If text already exists in the database, give an error and skip to end. - Fuzzy-match strings to topics and source. - If no potential match can be found to some of topics or source, give error and skip to end. - Ask user to confirm if the matched topics and source look okay. - if user says no, skip to end. - Actually insert the record. -} insertNote :: NoteRecord -> Connection -> IO () insertNote nr conn = do -- Check if it exists in the database already. status <- checkPreExistingText nr conn if status then putStrLn "Skipping... text exists already." else do -- Find best fit for all topics and source. -- See type signatures below. bestFitTopics <- fitTopics nr conn bestFitSource <- fitSource nr conn case any isNothing bestFitTopics of True -> putStrLn "Error... some topic couldn't be matched." False -> case bestFitSource of Nothing -> putStrLn "Error.. source couldn't be matched." _ -> do b <- isUserOkay nr bestFitTopics bestFitSource if b then do -- Create a new NoteRecord with matched -- and validated topics/source. nrValidated = nr { recordTopics = bestFitTopics , recordSource = bestFitSource } insertRow nrValidated conn else putStrLn "Abort due to user request." checkPreExistingText :: NoteRecord -> Connection -> Bool -- There are multiple topics in the NoteRecord. For each one, -- find the best fuzzy match, or indicate if there is no plausible -- match at all. fitTopics :: NoteRecord -> Connection -> [Maybe String] -- There is one source. Try to find fuzzy match. fitSource :: NoteRecord -> Connection -> Maybe String -- Present user with all fuzzy matches and get a yes/no response if it's -- okay to proceed. isUserOkay :: NoteRecord -> [Maybe String] -> Maybe String -> Bool -- Do actual insert into database. insertRow :: NoteRecord -> Connection -> IO ()