Haskell Formatting Issue

Question

main :: IO ()
main = do 
    contents <- readFile "text.txt"
    let database = (read contents :: [Film])
    putStr "Please enter your username: "
    userName <- getLine
    menu database        
    where menu newDb = do putStrLn "\nPlease select an option:"
                          putStrLn "1: Display all films currently in the database"
                          putStrLn "2: Add a new film to the database"
                          putStrLn "3: Search for films by director"
                          putStrLn "5: Exit"
                          putStr "\nSelected option: "
                          option <- getLine
                          case option of 
                                        "1" -> putStrLn(formatDatabase newDb)
                                        "2" -> do putStr "Name of film: "
                                               title <- getLine
                                               putStr "Name of director: "
                                               director <- getLine
                                               putStr "Year of release: "
                                               year <- getLine
                                               putStrLn(formatDatabase $ addFilm title director (read year) [] newDb)
                                        "3" -> do putStr "Name of director: "
                                               director <- getLine
                                               putStrLn $ formattedByDirector director
                          menu newDb

Returns error:

Parse error in pattern: putStr

On the line: "2" -> do putStr "Name of film: "

Daniel Fischer · Accepted Answer · 2012-05-02 14:17:48Z

5

You must indent the lines in the do block all to the level of the first token after the do. The same applies to the case 3.

case option of 
  "1" -> putStrLn(formatDatabase newDb)
  "2" -> do putStr "Name of film: "
            title <- getLine
            putStr "Name of director: "
            director <- getLine
            putStr "Year of release: "
            year <- getLine
            putStrLn(formatDatabase $ addFilm title director (read year) [] newDb)
  "3" -> do putStr "Name of director: "
            director <- getLine
            putStrLn $ formattedByDirector director

answered May 2, 2012 at 14:17

Daniel Fischer

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10 Comments

JamieB Over a year ago

This didn't resolve the issue, I still have the same error: Parse error in pattern: putStr

m09 Over a year ago

are you using tabs ? I read that 8 spaces tabs are assumed if that's the case. Maybe that's the source of your error.

m09 Over a year ago

I confirm that you have tabs in your code (at least in what you posted in your OP). Try replacing ALL YOUR TABS by spaces. Should run fine.

Daniel Fischer Over a year ago

@JamieB That looks correctly indented. But you never know with tabs, don't use tabs in Haskell code, configure your editor to indent with spaces.

m09 Over a year ago

BTW I suggest you tune your editor so that it uses spaces to simulate tabs (it's easily done in Notepad++). This way you won't be bothered later on. You can apply this behaviour only to .hs files quite easily if I'm not mistaken.

|

liyang · Accepted Answer · 2012-05-02 16:24:10Z

0

Please do not indent your code in the manner found in many textbooks. It looks nice on paper, but is terrible for actually working with.

Here's a much more sane style guide: https://github.com/tibbe/haskell-style-guide

answered May 2, 2012 at 16:24

liyang

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