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. $ ghci ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | 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 {handle: out} Prelude System.IO> GHC.Handle.hDuplicateTo h stdout -- as this point, GHCi goes quiet: I type ":quit" $ cat out Prelude System.IO> :quit Leaving GHCi. Cheers, Simon