Write sexps in Common Lisp format

[marnen]

Current situation

This gem has several Reader modules, in order to parse sexps with different syntaxes (Scheme, Common Lisp, SPARQL). However, it only has one Generator module, which doesn't all that work all that well for writing expressions that are to be parsed in a Common Lisp environment.

For example, we can read nil syntaxes for both Scheme and Common Lisp:

irb(main):017:0> SXP::Reader::Scheme.read '#n'
=> nil
irb(main):019:0> SXP::Reader::CommonLisp.read 'nil'
=> nil

...but we can't easily write a Ruby nil in a CLisp-friendly way:

irb(main):027:0> SXP::Generator.string(nil).chomp
=> "#n"

Proposed solution

It would be great to have Generator modules for the different syntaxes, perhaps something like this:

irb(main):027:0> SXP::Generator::Scheme.string(nil).chomp
=> "#n"
irb(main):028:0> SXP::Generator::CommonLisp.string(nil).chomp
=> "nil"

If this looks like something worthwhile, I can try implementing it and making a pull request.