lib/antelope/generation/tableizer.rb in antelope-0.1.8 vs lib/antelope/generation/tableizer.rb in antelope-0.1.9

@@ -36,10 +36,11 @@
       # @see #tablize
       # @see #conflictize
       def call
         tablize
         conflictize
+        defaultize
       end
 
       # Construct a table based on the grammar.  The table itself is
       # an array whose elements are hashes; the index of the array
       # corresponds to the state ID, and the keys of the hashes
@@ -65,11 +66,12 @@
                 table[state.id][look.name] <<
                   [:reduce, rule.production.id]
               end
 
               if rule.production.id.zero?
-                table[state.id][:"$"] = [[:accept, rule.production.id]]
+                table[state.id][:$end] =
+                  [[:accept, rule.production.id]]
               end
             end
           end
         end
 
@@ -92,11 +94,11 @@
               next
             end
 
             terminal = grammar.precedence_for(on)
 
-            rule_part, other_part = data.sort_by { |(t, d)| t }
+            rule_part, other_part = data.sort_by { |(t, _)| t }
 
             unless other_part[0] == :state
               $stderr.puts \
                 "Could not determine move for #{on} in state " \
                 "#{state} (reduce/reduce conflict)"
@@ -115,9 +117,35 @@
                 "#{state} (shift/reduce conflict)"
             when 1
               @table[state][on] = rule_part
             when -1
               @table[state][on] = other_part
+            end
+          end
+        end
+      end
+
+      # Reduce many transitions into a single `$default` transition.
+      # This only works if there is no `$empty` transition; if there
+      # is an `$empty` transition, then the `$default` transition is
+      # set to be the `$empty` transition.
+      #
+      # @return [void]
+      def defaultize
+        max = @table.map { |s| s.keys.size }.max
+        @table.each_with_index do |state|
+          if state.key?(:$empty)
+            state[:$default] = state[:$empty]
+          else
+            common = state.group_by { |k, v| v }.values.
+              sort_by(&:size).first
+
+            if common.size > (max / 2)
+              action = common[0][1]
+
+              keys = common.map(&:first)
+              state.delete_if { |k, _| keys.include?(k) }
+              state[:$default] = action
             end
           end
         end
       end
     end