Erlang and Elixir's colorful REPL shells

Question

How does Learn some Erlang or IEx colorize the REPL shell? Is kjell a stable drop-in replacement?

Answer 1

The way this is done in LYSE is to use a javascript plugin called highlight.js, so LYSE isn't actually doing it, your browser is. There are plugins/modes for most mainstream(ish) languages available for highlight.js. If the web is what you are interested in, this is one way to do it (except for when a user can't use JS or has it turned off).

This isn't actually the shell being highlighted at all, nor is it useful anywhere outside of browsers. I've been messing around with a way to do this more generically, initially by inserting static formatting in HTML and XML documents (feed it a document, and it outputs one with Erlang syntax highlighted a certain way whenever this is detected/tagged). I don't yet have a decent project to publish for this (very low on my priority list atm), but I can point you in the direction of some solid inspiration: the source for wx:demo.

Pay particular attention to the function demo:code_area/1. There you will see how the tokenization routines are used to provide highlight hints for the source code text display area in the wx:demo application. This can provide a solid foundation to build your own source highlighting/display utility. (I think it wouldn't be impossible, considering every terminal in common use today responds correctly to ANSI color codes, to write a plugin to the shell that highlights terminal input directly -- not that there is a big clamor for this feature at the moment.)

EDIT (Prompted by a comment by Fred the Magic Wonder Dog)

On the subject of ANSI color codes, if this is what you are actually after, they are easy to implement as a prepend to any string value you are returning within a terminal. The terminal escapes them, so you won't see the characters, but will perform whatever action the code represents. There is no termination (its not like a markup tag that encloses the text) and typically no concept of "default color to go back to" (though there are a gajillion-jillion extensions to telnet and terminal modes that enable all sorts of nonsense like this).

An example of basic colorization is the telcon:greet/0 and telcon:sys_help/0 functions in the v0.1 code of ErlMUD (along with a slew of other places -- colorization in games is sort of a thing). What you see there is a pre-built list per color, but this could be represented any way that would get those values at the front of the string. (I just happened to remember the code value sequences, but didn't remember the characters that make them up; the next version of the code represents this somewhat differently.) Here is a link to a list of ANSI color codes and a discussion about colorizing the shell. Play around! Its nerdy fun, 1980's style!

Oh, I almost forgot... if you really want to go down the rabbit hole without silly little child toys like ncurses to help you, take a look at termcap.