basic_set_bool.treetop

# Parsing Expression Grammar for basic boolean logic on a set of k -> { v1, v2, ... } elements.
# Amazing talk about Treetop and PEG's:  http://rubyconf2007.confreaks.com/d1t1p5_treetop.html
#
# lst = {
#   'foo' => [1, 2],
#   'bar' => [2, 3, 4],
#   'baz' => [5, 6]
# }
#
# require 'treetop'
# Treetop.load 'below_file'
# SetBoolParser.new.parse("! (foo && bar)").eval(lst)    # => [1, 3, 4, 5, 6]
# SetBoolParser.new.parse("foo || bar && baz").eval(lst) # => [1, 2]
# 
# -jf

grammar SetBoolGrammar
  rule logical_or
    lhs:logical_and space '||' space rhs:logical_or {
      def eval(set)
        lhs.eval(set) | rhs.eval(set)
      end
    }
    /
    logical_and
    /
    logical_not
  end

  rule logical_and
    lhs:logical_not space '&&' space rhs:logical_and {
      def eval(set)
        lhs.eval(set) & rhs.eval(set)
      end
    }
    /
    logical_not
  end

  rule logical_not
    '!' space rhs:primary {
      def eval(set)
        set.values.flatten - (rhs.eval(set) || [nil])
      end
    }
    /
    primary
  end

  rule primary
    key
    /
    '(' space logical_or space ')' {
      def eval(set)
        logical_or.eval(set)
      end
    }
  end

  rule key
    [a-zA-Z]+ {
      def eval(set)
        set[text_value]
      end
    }
  end

  rule space
    ' '*
  end
end