Move grammar parsing into new Grammar class

lib/propane.rb

@@ -5,6 +5,7 @@ require_relative "propane/code_point_range"
 require_relative "propane/fa"
 require_relative "propane/fa/state"
 require_relative "propane/fa/state/transition"
+require_relative "propane/grammar"
 require_relative "propane/lexer"
 require_relative "propane/lexer/dfa"
 require_relative "propane/parser"
@@ -36,12 +37,11 @@ class Propane
   end
 
   def initialize(input)
-    @tokens = {}
-    @rule_sets = {}
-    input = input.gsub("\r\n", "\n")
-    while !input.empty?
-      parse_grammar(input)
-    end
+    grammar = Grammar.new(input)
+    @classname = grammar.classname
+    @modulename = grammar.modulename
+    @tokens = grammar.tokens
+    @rule_sets = grammar.rule_sets
   end
 
   def generate(output_file, log_file)
@@ -58,44 +58,6 @@ class Propane
 
   private
 
-  def parse_grammar(input)
-    if input.slice!(/\A\s+/)
-      # Skip white space.
-    elsif input.slice!(/\A#.*\n/)
-      # Skip comment lines.
-    elsif input.slice!(/\Amodule\s+(\S+)\n/)
-      @modulename = $1
-    elsif input.slice!(/\Aclass\s+(\S+)\n/)
-      @classname = $1
-    elsif input.slice!(/\Atoken\s+(\S+)(?:\s+(\S+))?\n/)
-      name, pattern = $1, $2
-      if pattern.nil?
-        pattern = name
-      end
-      unless name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
-        raise Error.new("Invalid token name #{name}")
-      end
-      if @tokens[name]
-        raise Error.new("Duplicate token name #{name}")
-      else
-        @tokens[name] = Token.new(name, pattern, @tokens.size)
-      end
-    elsif input.slice!(/\Adrop\s+(\S+)\n/)
-      pattern = $1
-      @tokens[name] = Token.new(nil, pattern, @tokens.size)
-    elsif input.slice!(/\A(\S+)\s*:\s*\[(.*?)\] <<\n(.*?)^>>\n/m)
-      rule_name, components, code = $1, $2, $3
-      components = components.strip.split(/\s+/)
-      @rule_sets[rule_name] ||= RuleSet.new(rule_name, @rule_sets.size)
-      @rule_sets[rule_name].add_rule(components, code)
-    else
-      if input.size > 25
-        input = input.slice(0..20) + "..."
-      end
-      raise Error.new("Unexpected grammar input: #{input}")
-    end
-  end
-
   def expand_rules
     @rule_sets.each do |rule_name, rule_set|
       if @tokens.include?(rule_name)