diff --git a/2020/ruby/day_19.rb b/2020/ruby/day_19.rb
new file mode 100644
index 0000000..a57a7cc
--- /dev/null
+++ b/2020/ruby/day_19.rb
@@ -0,0 +1,67 @@
+# require "bundler/inline"
+
+# gemfile do
+#   source "https://rubygems.org"
+#   gem "parslet"
+# end
+
+rules, messages = ARGF.read.split("\n\n")
+
+# class Day19 < Parslet::Parser
+#   root(:rule_0)
+# end
+
+# rules = rules.split("\n").map {|rule| rule.split(": ") }.to_h
+# rules["8"] = "42 | 42 8"
+# rules["11"] = "42 31 | 42 11 31"
+# rules.each do |rule, sub_rules|
+#   sub_rules = sub_rules.split(" | ").map {|sub_rule|
+#     sub_rule.split(/\s+/).map {|sub_sub_rule|
+#       sub_sub_rule =~ /^\d+$/ ? "rule_#{sub_sub_rule}" : "str(#{sub_sub_rule})"
+#     }.join(" >> ")
+#   }.join(" | ")
+#   rule = "rule(:rule_#{rule}) { #{sub_rules} }"
+#   p rule
+
+#   Day19.class_eval(rule)
+# end
+
+# PARSER = Day19.new
+# def parsable?(input)
+#   !!PARSER.parse(input)
+# rescue
+#   false
+# end
+# puts messages.split("\n").select {|line| parsable?(line) }
+
+# begin
+#   p PARSER.parse("bbbbbbbaaaabbbbaaabbabaaa")
+# rescue Parslet::ParseFailed => failure
+#   puts failure.parse_failure_cause.ascii_tree
+# end
+
+rules = rules.split("\n").map {|line|
+  line.split(": ")
+}.to_h
+
+rule = rules["0"]
+while rule =~ /\d/
+  rule.gsub!(/\d+/) {|r|
+    case r
+    when "8"
+      "(?:42)+"
+    when "11"
+      "(?:#{(1..5).map {|i| (Array.new(i, "42") + Array.new(i, "31")).join(" ") }.join(" | ")})"
+    else
+      value = rules.fetch(r)
+      value = value[1..-2] if value =~ /^"\w+"$/
+      "(?:#{value})"
+    end
+  }
+end
+rule.gsub!(" ", "")
+while rule =~ /\(\?:\w+\)/
+  rule.gsub!(/\(\?:(\w+)\)/, '\1')
+end
+
+p messages.split("\n").count {|m| m =~ /^#{rule}$/ }