GHC as a library - getting output from GHCI
simonmarhaskell at gmail.com
Thu May 10 04:34:53 EDT 2007
Simon Peyton-Jones wrote:
> | Also if stmt =
> | SomeModule.prettyPrinter "foobar"
> | and SomeModule contains
> | prettyPrinter x = putStrLn $ "Pretty: " ++ x
> | then the let binding will not catch it.
> Indeed, that's exactly what I meant in my original msg. I have always thought it ugly that stdin and stdout are top-level definitions. I want to be able to say
> withStdout :: Handle -> IO a -> IO a
> so that (withStdout h a) runs 'a' but sends all std-out output to h.
> Haskell should support this. Starting a whole OS process to redirect stdout must surely be overkill!
And we do have support for this in GHC.
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.7, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base ... linking ... done.
Prelude> :m + System.IO
Prelude System.IO> h <- openFile "out" WriteMode
Prelude System.IO> GHC.Handle.hDuplicateTo h stdout
-- as this point, GHCi goes quiet: I type ":quit"
$ cat out
Prelude System.IO> :quit
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