GHCi in colour
m (→Prompt only: Corrected code markup)
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Latest revision as of 08:12, 28 September 2015
This page documents efforts to colourise GHCi output.
 1 Prompt only
The prompt can be colored by altering GHCi's
prompt setting including ANSI terminal color codes. For example
:set prompt "\ESC[34m\STX%s > \ESC[m\STX"
will give the prompt blue color:
As usual, adding this to
ghci.conf will auto-execute the command when running GHCi, making the prompt colored by default.
Remember to use
\STX to end an escape sequence. Without this control character, the prompt length will be computer incorrectly and your prompt will look wrong when editing long commands.
 2 Full highlighting
 2.1 Example
Or a type error:
Output like this would be the result of running, for example:
and would appear in the console/xterm as ansi terminal coloured output.
 2.2 Implementation
 2.2.1 Using sed and ghci.conf
You can use sed to color the non-prompt output, and color the prompt with ghci.conf. This works better than piping into HsColour for me. See this blog post for details.
This allows you to colorize everything you can catch with a regexp. Note that when coloring GHCi prompt using ghci.conf one should, in ultimate escapity, escape the escape codes with \001..\002, otherwise readline will mess up when editing long lines. For a working example of how this can be done refer to this example. Output:
This approach doesn't work well if you try to output an infinite sequence and then hit CTRL+C, ideas on how to fix that are welcome.
 2.2.2 Using HsColour
An existing tool, HsColour, could be modified to operate interactively. In fact, HsColour is already interactive, and with a small patch added on 2006-12-14 to control ouput buffering better, this works relatively nicely:
ghci 2>&1 | HsColour -tty
There are small delays however, when lexing certain tokens, and the interaction with readline isn't ideal.
 2.2.3 GuiHaskell
Neil Mitchell has a prototype gui haskell wrapper, based on gtk. Does this contain a reasonable ghci wrapper we could steal?
If you have an idea of how to do this nicely, add your proposal here.