How to - piping the output of one program to the input of another (capslocker) using emacs - haskell mode?

Question

capslocker.hs has following code:

import Control.Monad  
import Data.Char  
main = forever $ do  
    putStr "Give me some input: "  
    l <- getLine  
    putStrLn $ map toUpper l  

haiku.txt has following contents:

I'm a lil' teapot  
What's with that airplane food, huh?  
It's so small, tasteless 

In the terminal, I am able to do:

optimight@optimight:~$ cat haiku.txt  
I'm a lil' teapot  
What's with that airplane food, huh?  
It's so small, tasteless  

And this:

optimight@optimight:~$ cat haiku.txt | ./capslocker  
Give me some input: I'M A LIL' TEAPOT  
Give me some input: WHAT'S WITH THAT AIRPLANE FOOD, HUH?  
Give me some input: IT'S SO SMALL, TASTELESS  
Give me some input: capslocker: <stdin>: hGetLine: end of file 

How to test the same (as done in terminal) in emacs23 - haskell mode? Please guide.

Please note that, in emacs - haskell mode, I have tried following:

GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help  
Loading package ghc-prim ... linking ... done.  
Loading package integer-gmp ... linking ... done.  
Loading package base ... linking ... done.  
Prelude> :load "/home/optimight/capslocker.hs"  
[1 of 1] Compiling Main      ( /home/optimight/capslocker.hs, interpreted )  
Ok, modules loaded: Main.  
*Main> cat haiku.txt | ./capslocker  
<interactive>:3:15: parse error on input `|'   
*Main>

Answer 1

From the ghci prompt, you can call shell commands by prefixing with :!.

*Main> :! cat haiku.txt | ./capslocker

It ought to work the same in emacs.