Long standing annoying issue in ghci

[cheater00 cheater00]

A simple example of colored prompt would be good enough, so as not to make
the docs too huge. People will be able to figure out they need \STX, or
just make sure to tell them.

On Tue, 5 Dec 2017 23:17 Brandon Allbery, <allbery.b at gmail.com> wrote:

> It's indirectly already there:
> https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghci.html#the-ghci-and-haskeline-files
> Possibly an additional pointer needs to be in the FAQ/things to watch out
> for section.
>
> On Tue, Dec 5, 2017 at 5:13 PM, David Feuer <david at well-typed.com> wrote:
>
>> It sounds like this should be added to the GHCi documentation, even if
>> it's not strictly about GHCi.
>>
>>
>>
>> David Feuer
>> Well-Typed, LLP
>>
>> -------- Original message --------
>> From: Evan Laforge <qdunkan at gmail.com>
>> Date: 12/5/17 4:49 PM (GMT-05:00)
>> To: Brandon Allbery <allbery.b at gmail.com>
>> Cc: ghc-devs at haskell.org
>> Subject: Re: Long standing annoying issue in ghci
>>
>> Here's what I use:
>>
>> :set prompt "\ESC[46m\STX%s>\ESC[39;49m\STX "
>>
>> I believe \STX is a signal to haskeline for control sequences.
>> Documentation is here:
>> https://github.com/judah/haskeline/wiki/ControlSequencesInPrompt
>>
>> On Tue, Dec 5, 2017 at 12:57 PM, Brandon Allbery <allbery.b at gmail.com>
>> wrote:
>> > On Tue, Dec 5, 2017 at 12:36 PM, cheater00 cheater00 <
>> cheater00 at gmail.com>
>> > wrote:
>> >>
>> >> without color coding the prompt so I can't really turn it off. It
>> >> seems like a simple arithmetic issue somewhere in the readline
>> >> implementation.
>> >
>> >
>> > It's not arithmetic except in the sense that it's not doing *any* math.
>> > Color codes in a terminal are necessarily implemented as character
>> sequences
>> > (this is pretty much the definition of a terminal interface), and
>> haskeline
>> > makes no effort to recognize them, so it treats them the same as
>> displayed
>> > character sequences and skips over them as if they were displayed
>> > characters.
>> >
>> > GNU readline handles this by recognizing the character mode sequences
>> as not
>> > taking up character positions (this is more complex than you think given
>> > that GNU readline doesn't assume all terminals obey the ANSI standard;
>> as it
>> > turns out, neither does haskeline, so it actually gets a bit nasty), and
>> > recognizing the special behavior of carriage return, and providing \[ \]
>> > escapes to declare the sequence inside as "invisible" to to character
>> > positioning (and it's on the person crafting the prompt to insure that
>> it
>> > actually is). Beyond that, it'd actually have to implement a 'terminal
>> > emulator' internally to get it right in all cases --- and i'd be on the
>> user
>> > to ensure their declared terminal type matches the actual one well
>> enough
>> > for the 'terminal emulator' to reflect the terminal's actual behavior,
>> so
>> > it'd be a potential source of even weirder behavior.
>> >
>> > So, (a) haskeline issue, not strictly ghc/ghci, and (b) not really
>> fixable,
>> > but partially work-around-able for common cases.
>> >
>> > --
>> > brandon s allbery kf8nh                               sine nomine
>> associates
>> > allbery.b at gmail.com
>> ballbery at sinenomine.net
>> > unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
>> >
>> > _______________________________________________
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>> >
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>
>
>
> --
> brandon s allbery kf8nh                               sine nomine
> associates
> allbery.b at gmail.com
> ballbery at sinenomine.net
> unix, openafs, kerberos, infrastructure, xmonad
> http://sinenomine.net
> _______________________________________________
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