class Predicate
  class ToRubyCode < Sexpr::Processor

    def on_tautology(sexpr)
      "true"
    end

    def on_contradiction(sexpr)
      "false"
    end

    def on_qualified_identifier(sexpr)
      "#{sexpr.qualifier}[:#{sexpr.name}]"
    end

    def on_identifier(sexpr)
      if s = options[:scope]
        "#{s}[:#{sexpr.last.to_s}]"
      else
        sexpr.last.to_s
      end
    end

    def on_not(sexpr)
      "#{sexpr.operator_symbol}" << apply(sexpr.last, sexpr)
    end

    def on_nadic_bool(sexpr)
      sexpr.sexpr_body.map{|term|
        apply(term, sexpr)
      }.join(" #{sexpr.operator_symbol} ")
    end
    alias :on_and :on_nadic_bool
    alias :on_or  :on_nadic_bool

    def on_dyadic(sexpr)
      sexpr.sexpr_body.map{|term|
        apply(term, sexpr)
      }.join(" #{sexpr.operator_symbol} ")
    end
    alias :on_eq  :on_dyadic
    alias :on_neq :on_dyadic
    alias :on_lt  :on_dyadic
    alias :on_lte :on_dyadic
    alias :on_gt  :on_dyadic
    alias :on_gte :on_dyadic

    def on_in(sexpr)
      "#{to_ruby_literal(sexpr.values)}.include?(#{apply(sexpr.identifier)})"
    end

    def on_literal(sexpr)
      to_ruby_literal(sexpr.last)
    end

  protected

    def to_ruby_literal(x)
      x.inspect
    end

    def apply(sexpr, parent = nil)
      code = super(sexpr)
      if parent && (parent.priority >= sexpr.priority)
        code = "(" << code << ")"
      end
      code
    end

  end
end