Random sequence generator program

random.hs

{-|
    Random sequence generator program
    Copyright (C) 2017  Valdemar Lindberg

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

-}
import System.Exit
import System.Random
import System.Environment
import System.IO
import Data.Time

-- Check if argument sequence is valid.
checkArgument :: [String] -> Bool
checkArgument args = do
                let mi = read (args!!0) :: Int
                let mx = read (args!!1) :: Int
                let n  = read (args!!2) :: Int
                if mi > mx
                    then False
                else if n < 0
                    then False
                else True

-- Get current time of epoch.
getTime :: IO Int
getTime = do
  currTime <- getCurrentTime
  let timed = floor $ utctDayTime currTime
  return timed

-- Generate random number sequence
generateRandom :: [String] -> IO [String]
generateRandom args = do
                    let mi = read (args!!0) :: Int
                    let mx = read (args!!1) :: Int
                    let n  = read (args!!2) :: Int
                    seed <- getTime
                    let g = mkStdGen seed
                    return [ show x | x <- (take n (randomRs (mi, mx) g))]

main = do
    args <- getArgs
    if length(args) /= 3
        then do
            print("Requires 3 argument | min max n.\n")
            exitFailure
    else do
        if not (checkArgument args)
            then do
                print("Invalid arguments.\n")
                exitFailure
        else do
            randseq <- ( generateRandom args )
            mapM_ putStrLn randseq
            exitSuccess