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"