Prettier Predicates

A quick fix to the DSL to support predicates with zero arity without the need for brackets. Example:

db = RubyProlog.new do
  tags['fire'].fact
  tags['paper'].fact

  # BEFORE:
  # is_lit[] << tags['fire']
  # AFTER:
  is_lit << tags['fire']
end

# BEFORE:
# db.query{ is_lit[] }  #=> [{}]
# AFTER:
db.query{ is_lit }  #=> [{}]

What is false?

Added support for using false in your predicates. Quick examples:

db = RubyProlog.new do
  foo[:_] << [false]
  foo['x'].fact

  bar[:_] << [:CUT, false]
  bar['x'].fact

  baz[false].fact
end

db.query{ foo['x'] }   #=> [{}]
db.query{ bar['x'] }   #=> []
db.query{ baz[false] } #=> [{}]

Sanding off some rough edges and then some

• ruby-prolog now supports Prolog's underscore _ as a symbol :_, for all your any-matching needs.
• Instances of ruby-prolog now support .clone. This is useful for defining a base set of facts to clone multiple times (e.g. for every HTTP request), add facts to it, and discard it afterwards.
• Creating a new instance has a slightly nicer syntax.
• Fixed some to_prolog bugs.

New API and a few features

• Querying now returns an array of all variable solutions. You also now query outside the instance_eval. See this test for a good example.
• Added a new not_ predicate, corresponding to Prolog's \+
• Added .to_prolog in case you want to copy/paste your RubyProlog definitions into another Prolog environment.