rewrite_block_pass (UnifiedRuby)

    # File lib/unified_ruby.rb, line 40
      def rewrite_block_pass exp
        if exp.size == 3 then
          _, block, recv = exp
          case recv.first
          when :super then
            recv << s(:block_pass, block)
            exp = recv
          when :call then
            recv.last << s(:block_pass, block)
            exp = recv
          else
            raise "huh?: #{recv.inspect}"
          end
        end

        exp
      end