scheme: add support for Racket

[cwfoo]

Add support for the Racket language.

The Scheme parser could be reused for Racket. Racket file extensions (e.g. *.rkt) could be added to these lines:

ctags/parsers/scheme.c

Lines 113 to 118 in e522743

	static const char *const extensions [] = {
	"SCM", "SM", "sch", "scheme", "scm", "sm", NULL
	};
	static const char *const aliases [] = {
	"gosh", "guile", NULL
	};

[masatake]

Could you open a pull request?

[masatake]

I don't know Racket well.

As far as reading its web site quikcly, racket can switch grammer (syntax?) for the input file with #lang notation. So choosing the scheme parser for ".rkt" file doesn't make good result.

What we need is a Rapcker parser which recognizes #lang notation and run a proper subparser.
http://docs.racket-lang.org/search/index.html?q=H%3A

Which non-S-exp language is popoular as Racker language extentsion?
datalog?

[cwfoo]

Racket is practically always written using s-expressions. I believe people only switch syntax for experiments. I think the Scheme parser is sufficient. Otherwise, you would need to maintain a huge number of subparsers that aren't used by many people (e.g. a parser for Algol 60, parsers for the endless list of experimental languages made by the Racket community).

Which non-S-exp language is popular as Racket language extension?

There aren't really any. The only mainstream one is the Scribble language (#lang scribble) used for Racket documentation, and it has a separate file extension (*.scrbl).

[masatake]

I see. Thank you.

[masatake]

Solved by #2315. Sorry to be late for solving this issue.
Scribble language is interesting but it is not the time for working for the language.