CODEWITHSUNDEEP
listsortinghaskellinputfilter
seph
seph

Reputation: 77

Haskell: filter and sort using input values

so I'm creating a program that will pick one of two libraries (audio.lhs or video.lhs) and will return a pdf with a list ordered and filtered by a given category: 

mymain = do {putStrLn "What do you wanna search, Video or Audio?";  
          tipo <- getLine;   
          if tipo == "Audio"  
          then do {  
          a <- readFile "audio.lhs" ;  
          let text = splitEvery 7 (splitRegex (mkRegex "\t") a)  
              list = map musicFile text  
              select = filter ((>1000) .size) list  
              orderList = sortBy (comparing title)   
              dir = Dir orderList  
              hs =    "import Dir\nimport TeX\nimport System.Cmd"  
                   ++ "\ntoTeX= do { writeFile \"out.tex\" $ prettyprint dat ;"  
                   ++ "system \"pdflatex out\"}"  
                   ++ "\ndat="  
                   ++ show dir  
          in do { writeFile "dat.hs" hs ;  
                  putStrLn "\nOk.\nNow load \'dat.hs\' and run \'toTeX\'\n"  
                }}...

Everything is running but now i need that the functions 

select = filter ((>1000) .size) list

and

orderList = sortBy (comparing title)

instead of working with values that are given by me, i want them to work with values choosen by the user of the program (inputs), so if he wants to filter files that are >2000 or <500 is his choice and same with the category,size or title or another thing.

My data structure is 

data File = File {
 filename :: String ,
 size :: Int ,
 filetype :: String ,
 copyright :: String ,
 title :: String ,
 artist :: String ,
 year :: String } deriving Show

and 

musicFile :: [String] -> File  
musicFile [name, size, tipo, copy, title, artist, year] = File name (read size) tipo copy title artist year

Any help would be gladly appreciated.

Thanks in advance.

Upvotes: 0

Views: 603

Answers (1)

Daniel Wagner
Daniel Wagner

Reputation: 152837

The simplest mechanism available in Haskell for parsing strings is the Read typeclass. Instances of this class have enough functionality to implement

read   :: (Read a) => String -> a
readLn :: (Read a) => IO a

either of which should be enough to get you started on your way to reading an Int (which is an instance of Read) from input.

Upvotes: 2

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