1 files changed, 63 insertions, 0 deletions
diff --git a/tool/lrama/lib/lrama/counterexamples/derivation.rb b/tool/lrama/lib/lrama/counterexamples/derivation.rb
new file mode 100644
index 0000000000..691e935356
--- /dev/null
+++ b/tool/lrama/lib/lrama/counterexamples/derivation.rb
@@ -0,0 +1,63 @@
+module Lrama
+  class Counterexamples
+    class Derivation
+      attr_reader :item, :left, :right
+      attr_writer :right
+
+      def initialize(item, left, right = nil)
+        @item = item
+        @left = left
+        @right = right
+      end
+
+      def to_s
+        "#<Derivation(#{item.display_name})>"
+      end
+      alias :inspect :to_s
+
+      def render_strings_for_report
+        result = []
+        _render_for_report(self, 0, result, 0)
+        result.map(&:rstrip)
+      end
+
+      def render_for_report
+        render_strings_for_report.join("\n")
+      end
+
+      private
+
+      def _render_for_report(derivation, offset, strings, index)
+        item = derivation.item
+        if strings[index]
+          strings[index] << " " * (offset - strings[index].length)
+        else
+          strings[index] = " " * offset
+        end
+        str = strings[index]
+        str << "#{item.rule_id}: #{item.symbols_before_dot.map(&:display_name).join(" ")} "
+
+        if derivation.left
+          len = str.length
+          str << "#{item.next_sym.display_name}"
+          length = _render_for_report(derivation.left, len, strings, index + 1)
+          # I want String#ljust!
+          str << " " * (length - str.length)
+        else
+          str << " • #{item.symbols_after_dot.map(&:display_name).join(" ")} "
+          return str.length
+        end
+
+        if derivation.right&.left
+          length = _render_for_report(derivation.right.left, str.length, strings, index + 1)
+          str << "#{item.symbols_after_dot[1..-1].map(&:display_name).join(" ")} "
+          str << " " * (length - str.length) if length > str.length
+        elsif item.next_next_sym
+          str << "#{item.symbols_after_dot[1..-1].map(&:display_name).join(" ")} "
+        end
+
+        return str.length
+      end
+    end
+  end
+end