Add p_parse_*() API for each start rule

lib/propane/generator.rb

@@ -71,14 +71,15 @@ class Propane
         end
         tokens_by_name[token.name] = token
       end
-      # Check for user start rules.
-      @grammar.start_rules.each_with_index do |start_rule, i|
+      # Create real start rule(s).
+      real_start_rules = @grammar.start_rules.map do |start_rule|
         unless @grammar.rules.find {|rule| rule.name == start_rule}
           raise Error.new("Start rule `#{start_rule}` not found")
         end
-        # Add "real" start rule.
-        @grammar.rules.unshift(Rule.new("$#{start_rule}", [start_rule, "$EOF"], nil, nil, nil))
+        Rule.new("$#{start_rule}", [start_rule, "$EOF"], nil, nil, nil)
       end
+      # Add real start rules before user-given rules.
+      @grammar.rules = real_start_rules + @grammar.rules
       # Generate and add rules for optional components.
       generate_optional_component_rules!(tokens_by_name)
       # Build rule sets.

lib/propane/grammar.rb

@@ -11,7 +11,7 @@ class Propane
     attr_reader :free_token_node
     attr_reader :modulename
     attr_reader :patterns
-    attr_reader :rules
+    attr_accessor :rules
     attr_reader :start_rules
     attr_reader :tokens
     attr_reader :code_blocks

lib/propane/parser.rb

@@ -16,11 +16,20 @@ class Propane
       @warnings = Set.new
       @errors = Set.new
       @options = options
-      start_item = Item.new(grammar.rules.first, 0)
-      eval_item_sets = Set[ItemSet.new([start_item])]
+      start_items = grammar.rules[0...grammar.start_rules.length].map do |start_rule|
+        Item.new(start_rule, 0)
+      end
+      start_item_sets = start_items.map {|item| ItemSet.new([item])}
+      eval_item_sets = Set[*start_item_sets]
 
       while eval_item_sets.size > 0
-        item_set = eval_item_sets.first
+        item_set =
+          if start_item_sets.size > 0
+            # Ensure we evaluate start_item_sets first in order
+            start_item_sets.slice!(0)
+          else
+            eval_item_sets.first
+          end
         eval_item_sets.delete(item_set)
         unless @item_sets_set.include?(item_set)
           item_set.id = @item_sets.size