todo.haskell

todo.hs

--my first real haskell app

import System.Environment
import System.Directory
import System.IO
import Data.List

dispatch :: [(String, [String] -> IO ())]
dispatch = [
  ("add",add),
  ("view",view),
  ("remove",remove)
  ]

main = do
  (command:args) <- getArgs
  let (Just action) = lookup command dispatch
  action args

add :: [String] -> IO ()
add [filename, todoItem] = appendFile filename (todoItem ++ "\n")

view :: [String] -> IO ()
view [filename] = do
  contents <- readFile filename
  let todoTasks = lines contents
      numberedTasks = zipWith (\n line -> show n ++ "-" ++ line) [0..] todoTasks
  putStr $ unlines numberedTasks

remove :: [String] -> IO ()
remove [filename, numberString] = do
  handle <- openFile filename ReadMode
  (tempName, tempHandle) <- openTempFile "." "temp"
  content <- hGetContents handle
  let number = read numberString
      todoTasks = lines content
      newTodoItems = delete (todoTasks !! number) todoTasks
  hPutStr tempHandle $ unlines newTodoItems
  hClose tempHandle
  hClose handle
  removeFile filename
  renameFile tempName filename