GHC as a library - getting output from GHCI

[Matthew Danish]

On Wed, May 09, 2007 at 10:48:15PM +0200, Mads Lindstr?m wrote:
> Hi
> 
> Look at System.Posix.IO
> 
> I do not know if that module can do what you want. But it does deal with
> FileDescriptors and handles.
> 
> Maybe the dup function can help you. According to
> http://www2.lib.uchicago.edu/~keith//tcl-course/topics/processes.html it
> does:
> 
> "The dup implements the dup system call, which duplicates one desired
> open file descriptor into another. This can be used connect standard
> input or standard output to a pipe. This sample code shows how a parent
> process can fork the standard Unix sort command and then feed it data to
> be sorted. A simple extension would allow the child to write the results
> back to the parent."
> 
> But I have not tested it yet, and I am not really familiar with Unix
> inter-process communication.
> 

Right, good thinking.  This is what I've come up with for Unix-only:

> module WrapIO where
> import System.IO
> import System.Posix.IO
> import Control.Exception

> wrapIO :: IO a -> IO (a, String)
> wrapIO action = do
>   oldStdOutput <- dup stdOutput
>   (rd, wr)     <- createPipe
>   dupTo wr stdOutput
>   v <- action
>   h <- fdToHandle rd
>   closeFd wr
>   s <- hGetContents h
>   return (v, s)
>     `finally` do 
>         dupTo oldStdOutput stdOutput
>         closeFd oldStdOutput

Unfortunately, dupTo will not work on Win32 afaik.

-- 
-- Matthew Danish -- user: mrd domain: cmu.edu
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