Split grammar statement parsing into separate methods

lib/propane/grammar.rb

@@ -28,15 +28,45 @@ class Propane
 
     def parse_statement!
       @next_line_number = @line_number
-      if consume!(/\A\s+/)
-        # Skip white space.
-      elsif consume!(/\A#.*\n/)
-        # Skip comment lines.
-      elsif md = consume!(/\Amodule\s+(\S+)\s*;/)
+      if parse_white_space!
+      elsif parse_comment_line!
+      elsif parse_module_statement!
+      elsif parse_class_statement!
+      elsif parse_token_statement!
+      elsif parse_tokenid_statement!
+      elsif parse_drop_statement!
+      elsif parse_rule_statement!
+      else
+        if @input.size > 25
+          @input = @input.slice(0..20) + "..."
+        end
+        raise Error.new("Unexpected grammar input at line #{@line_number}: #{@input.chomp}")
+      end
+      @line_number = @next_line_number
+    end
+
+    def parse_white_space!
+      consume!(/\A\s+/)
+    end
+
+    def parse_comment_line!
+      consume!(/\A#.*\n/)
+    end
+
+    def parse_module_statement!
+      if md = consume!(/\Amodule\s+(\S+)\s*;/)
         @modulename = md[1]
-      elsif md = consume!(/\Aclass\s+(\S+)\s*;/)
+      end
+    end
+
+    def parse_class_statement!
+      if md = consume!(/\Aclass\s+(\S+)\s*;/)
         @classname = md[1]
-      elsif md = consume!(/\Atoken\s+(\S+?)(?:\s+([^\n]+?))?\s*(?:;|<<\n(.*?)^>>\n)/m)
+      end
+    end
+
+    def parse_token_statement!
+      if md = consume!(/\Atoken\s+(\S+?)(?:\s+([^\n]+?))?\s*(?:;|<<\n(.*?)^>>\n)/m)
         name, pattern, code = *md[1, 3]
         if pattern.nil?
           pattern = name
@@ -54,17 +84,29 @@ class Propane
         end
         pattern = Pattern.new(pattern: pattern, token: token, line_number: @line_number, code: code, code_id: code_id)
         @patterns << pattern
-      elsif md = consume!(/\Atokenid\s+(\S+?)\s*;/m)
+      end
+    end
+
+    def parse_tokenid_statement!
+      if md = consume!(/\Atokenid\s+(\S+?)\s*;/m)
         name = md[1]
         unless name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
           raise Error.new("Invalid token name #{name.inspect}")
         end
         token = Token.new(name: name, id: @tokens.size, line_number: @line_number)
         @tokens << token
-      elsif md = consume!(/\Adrop\s+(\S+)\s*;/)
+      end
+    end
+
+    def parse_drop_statement!
+      if md = consume!(/\Adrop\s+(\S+)\s*;/)
         pattern = md[1]
         @patterns << Pattern.new(pattern: pattern, line_number: @line_number, drop: true)
-      elsif md = consume!(/\A(\S+)\s*->\s*([^\n]*?)(?:;|<<\n(.*?)^>>\n)/m)
+      end
+    end
+
+    def parse_rule_statement!
+      if md = consume!(/\A(\S+)\s*->\s*([^\n]*?)(?:;|<<\n(.*?)^>>\n)/m)
         rule_name, components, code = *md[1, 3]
         unless rule_name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
           raise Error.new("Invalid rule name #{name.inspect}")
@@ -72,13 +114,7 @@ class Propane
         components = components.strip.split(/\s+/)
         # Reserve rule ID 0 for the "real" start rule.
         @rules << Rule.new(rule_name, components, code, @line_number, @rules.size + 1)
-      else
-        if @input.size > 25
-          @input = @input.slice(0..20) + "..."
-        end
-        raise Error.new("Unexpected grammar input at line #{@line_number}: #{@input.chomp}")
       end
-      @line_number = @next_line_number
     end
 
     # Check if the input string matches the given regex.