If you simplify your DOS prompt:
>prompt $G
then it doesn't show you but it does leave more space for typing.
Right. The program looks like this:-
module Main
where
import System.Directory(getCurrentDirectory)
main = do
pwd <- getCurrentDirectory
putStr pwd
This goes in a file main.hs and defines the main indeed only module with the entry point main.
To get access to the required system call we import the system library called System.Directory but specify (in the brackets) that the only reference we want to make is to the function getCurrentDirectory.
Now our main function consists of two IO actions that are stacked one on top of the other inside the do construct, which has the overall effect of taking the first action and then the second.
The first action calls the system function getCurrentDirectory and assigns the identifier pwd to the result.
The type of getSystemDirectory is
getCurrentDirectory :: IO FilePath
In other words it's an IO action that returns a value of type FilePath - and FilePath is just a synonym for the String type, so we can display this without further manipulation using a function that takes a string parameter.
So the second action prints the value of pwd to the terminal.
ok now to compile - compile the file main.hs and specify the output file to be called pwd.exe:
>dir
Volume in drive C has no label.
Volume Serial Number is 6496-80C4
Directory of C:\Users\polly\Documents\Projects\Haskell\pwd
20/05/2015 21:17 <DIR> .
20/05/2015 21:17 <DIR> ..
20/05/2015 21:17 131 main.hs
20/05/2015 21:04 112 main.hs~
20/05/2015 21:16 1,389 notes.txt
20/05/2015 21:14 1,309 notes.txt~
4 File(s) 2,941 bytes
2 Dir(s) 273,825,931,264 bytes free
>ghc main.hs -o pwd.exe
[1 of 1] Compiling Main ( main.hs, main.o )
Linking pwd.exe ...
Now I can run it and see my working directory:
>pwd
C:\Users\polly\Documents\Projects\Haskell\pwd
>
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