getting the program arguments

Question

I need to get program arguments and show them

module Main ( main ) where

import System ( getArgs )

main = do

 args<-getArgs

 print $ show args

But it does nothing.Maybe my call incorrect?

>main 3 4

What's `main 3 4`? Is it how you invoke the compiled program from the command line? — , Oct 20 '11 at 19:27
$ ./test one two three "[\"one\",\"two\",\"three\"]" works for me just fine. — alf, Oct 20 '11 at 19:28
I made this program then called it from ghc this way main 3 4. but .hs name - number6+1.hs — Артём Царионов, Oct 20 '11 at 19:31
maybe you're not compiling it right. What does `$ runhaskell main.hs one two three` do for you? — rampion, Oct 20 '11 at 19:51
By the way, `print $ show` is unnecessary. Look at the type of `print`. — Tyler, Oct 20 '11 at 20:11

score 3 · Answer 1 · answered Oct 20 '11 at 22:55

3

It sounds like you're trying to run the program from within GHCi. In that case, you can use the :main command to run your program with arguments.

*Main> :main foo bar
"[\"foo\",\"bar\"]"

answered Oct 20 '11 at 22:55

hammar

score 0 · Accepted Answer · answered Oct 20 '11 at 19:57

0

Try changing 'System' -> 'System.Environment':

module Main ( main ) where
import System.Environment ( getArgs )

main = do
  args <- getArgs
  mapM putStrLn args

answered Oct 20 '11 at 19:57

barti_ddu

1

`ghc --make Main` and `Main.exe arg1 arg2` – barti_ddu Oct 20 '11 at 20:07
1

@Артём Царионов: guess you are calling `ghci` (interpreter), not `ghc` which is compiler... Run cmd, navigate to your source dir and execute `ghc --make Main` – barti_ddu Oct 20 '11 at 20:27
@Артём Царионов: anyway, you'd better import `System.Environment` (afair, ghc switched to new import locations from 7.2 completely) http://www.haskell.org/hoogle/?hoogle=getargs – barti_ddu Oct 20 '11 at 21:18
@Артём Царионов: in WinGhci you can compile with `:! ghc --make number6+2` – franza Oct 20 '11 at 21:23

2 Answers2