This small program was the first real program I wrote in Haskel. The only reason why I put it here is the possibility to receive feedback about the abundant inconsistencies, unsafeties and not very elegant decisions which the code provide to learn and leave them behind next time

sctl-gist.hs

-- This small program was the first real program I wrote in Haskel. The
-- only reason why I put it here is the possibility to receive feedback
-- about the abundant inconsistencies, unsafeties and not very elegant
-- decisions which the code provide to learn and leave them behind next
-- time

import Options.Applicative
import System.Environment
import System.Exit
import System.Process
import Data.List (isInfixOf)
import Text.Regex.PCRE

-- parser with optparse-applicative

data Options = Options 
  { extDisplay :: Bool
  , lapDisplay :: Bool }

options :: Parser Options 
options = Options 
     <$> switch
         ( long "external-display"
        <> short 'e'
        <> help "turn on the external display connected to the laptop" )
     <*> switch
         ( long "local-display"
        <> short 'l'
        <> help "turn on the local display of the laptop" )

greet :: Options -> IO () 
greet (Options True False) = getDisplays >>= setDisplays 'e'
greet (Options False True) = getDisplays >>= setDisplays 'l'
greet _ = getDisplays >>= setDisplays 'n'

main :: IO ()
main = execParser opts >>= greet 
  where
    opts = info (helper <*> options) 
      ( fullDesc
     <> progDesc "Switch between local and external displays"
     <> header "sctl - a small tool to switch between screen set-ups in a quick way" )

-- programm code

data Screen = Screen { display :: String
                     , connected :: Bool
                     , active :: Bool
                     } deriving (Show)

getDisplays :: IO [Screen]
getDisplays = do
            output <- readProcess "xrandr" [] ""
            let oLines      = lines output
            let displayStrs = fmap words ((filter (\line -> isInfixOf " connected " line) oLines))
            let scrData     = fmap (\display -> Screen (display !!0)
                                                       (display !!1 == "connected")
                                                       ((concat display) =~ "axis\\)\\d{3}" :: Bool))
                                   displayStrs -- parse active with regular expr
            return scrData

setDisplays :: Char -> [Screen] -> IO()
setDisplays mode displays
    | mode == 'l' = displayOn [(head displays)] >> displayOff (tail displays)
    | mode == 'e' = displayOn (tail displays) >> displayOff [(head displays)]
    | mode == 'n' = if (length displays) > 1 then displayOn notrunning >> displayOff running else return ()
    where
      displayOn on   = mapM_ (\id -> callProcess "xrandr" ["--output", display id, "--auto"]) on 
      displayOff off = mapM_ (\id -> callProcess "xrandr" ["--output", display id, "--off"]) off
      running        = filter (\dis -> active dis == True) displays
      notrunning     = filter (\dis -> active dis == False) displays