Simple terminal task manager

todo.hs

module Main where

import System.Environment( getArgs )
import System.IO
import Control.Monad
import Data.List.Split

main = do
	args <- getArgs
	mapM execute_command (split_commands args)

execute_command :: (String, [String]) -> IO ()
execute_command ("-add", args) = todo_add_item args
execute_command ("-show", args) = todo_show args
execute_command ("-rm", args) = todo_remove args 
execute_command (_, _) = return ()

split_commands :: [String] -> [(String, [String])]
split_commands [] = []
split_commands (x:xs) = (x, takeWhile is_not_command xs):(split_commands $ dropWhile is_not_command xs)
	where
		is_not_command a = head a /= '-'


todo_add_item :: [String] -> IO ()
todo_add_item [] = return ()
todo_add_item (x:xs) = do 
					appendFile "todo.txt" (x ++ "\n") 
					todo_add_item xs

todo_show :: [String] -> IO ()
todo_show _ = do 
			contents <- readFile "todo.txt"
			let output = zipWith (\t n -> (show n) ++ ") " ++ t) (lines contents) [1..]
			putStr $ unlines output
			return ()

todo_remove :: [String] -> IO ()
todo_remove xs = do
				let ns = map (\a -> read a :: Int) xs
				contents <- readFile "todo.txt"
				length contents `seq` (writeFile "todo.txt" $ remove_all ns contents)
				return ()

remove_one :: Int -> String -> String
remove_one n contents = unlines $ take (n-1) (lines contents) ++ (drop n (lines contents))

remove_all :: [Int] -> String -> String
remove_all [] contents = contents
remove_all (n:ns) contents = remove_one n (remove_all ns contents)