GHCi 6.12.3 stdout redirection works for :type, but not for :info

[Claus Reinke]

> good diagnosis.  want to make a ticket?

done:

    http://hackage.haskell.org/trac/ghc/ticket/4332

On second thought: is there any reason to use haskelline for
*output*, as opposed to *input* history logging/editing?

If not, avoiding that might be the easiest fix.

Claus

> | -----Original Message-----
> | From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-
> | users-bounces at haskell.org] On Behalf Of Claus Reinke
> | Sent: 22 September 2010 16:05
> | To: GHC users
> | Subject: Re: GHCi 6.12.3 stdout redirection works for :type, but not for
> | :info
> |
> |
> | > The problem is that my code for redirecting the output
> | > of GHCi commands still works for things like :type, but
> | > no longer for things like :info (this is my smallest example
> | > demonstrating the effect).
> |
> | The difference seems to be between commands that use
> | old-style GHCi output (works with redirection) versus
> | commands that output via Haskelline (redirection fails).
> |
> | ':type' calls typeOfExpr, which still uses 'printForUser',
> | which ultimately goes down to
> | 'compiler/utils/Pretty.lhs:printDoc', where it just calls
> | 'hPutChr/Str stdout'.
> |
> | ':info' calls 'info', which uses 'outputStrLn', which
> | ultimately goes down to
> | 'Haskelline/Backend/Win32.hsc:putOut', where it
> | calls either 'WriteConsole' (if to terminal), or
> | 'Data.ByteString.putStr' (no terminal).
> |
> | The distinction between terminal and no terminal
> | is currently done only once per GHCi session, so
> | redirecting stdout to a file for just one command
> | will call 'WriteConsole' on a non-terminal handle
> | (redirecting the whole session works, though it is
> | useless for writing advanced GHCi commands).
> |
> | I consider this a serious GHCi regression (never
> | mind the inconsistencies between GHCi commands),
> | as it breaks all the nice .ghci goodies from my old
> | tutorial (*) that people keep writing to me about.
> |
> | If this analysis is correct, possible fixes would be:
> |
> | - use 'printForUser/outputStrLn' consistently
> |     (why is the latter needed for some commands,
> |     but not for others?), and ensure that terminal
> |     status is checked for each GHCi command,
> |     instead of once per session (the main problem
> |     is the version of 'putOut' that goes into the
> |     'RunTerm structure's 'putStrOut' field - it is
> |     set by 'myRunTerm' in 'runInputTWithPrefs')
> |
> | - expose a GHCi command that allows users
> |     to trigger Haskelline's terminal status check,
> |     and rewrite the redirection code accordingly
> |
> | Sadly, I won't be able to implement either myself
> | at the moment - is there a chance of getting this
> | fixed for the 7.0.1 release (the first variant would
> | be the proper fix, the second variant a quick hack
> | to restore functionality)?
> |
> | Claus
> |
> | (*) http://haskell.org/haskellwiki/Ghci#Using_.ghci.2C_a_mini-tutorial
> |
> | > With the attached GHCi script defining a
> | >
> | >    :redir <var> <command>
> | >
> | > command that should redirect the ouput of <command>
> | > into variable <var>, we get the output appended below
> | > (note the Exception for WriteConsole "handle is invalid",
> | > which is written into the temporary file when :info is
> | > called while stdout is redirected to that temporary file;
> | > in other words, the error message appears where the
> | > output of the command fails to appear).
> | >
> | > Is that an expected change with a known workaround,
> | > so that I just need to update my code, or is that
> | > unexpected behaviour that can only be fixed in GHCi?
> | >
> | > Claus
> | >
> | > PS. This is on Windows 7, if that matters.
> | >
> | > ------------- example session output
> | > $ ghcii.sh -ignore-dot-ghci
> | > GHCi, version 6.12.3: http://www.haskell.org/ghc/  :? for help
> | > ..
> | > Prelude> :cmd readFile "redir.script"
> | > Prelude> :redir x :t map
> | > ..
> | > Prelude> x
> | > "-- logging GHCi stdout\nmap :: (a -> b) -> [a] -> [b]\n"
> | > Prelude> :redir y :i map
> | > Prelude> y
> | > "-- logging GHCi stdout\n*** Exception: WriteConsole: invalid argument
> | > (Das
> | > Handle ist ung\252ltig.)\n"
> | >
> |
> |
> |
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