refactor Lexer to only take StringScanner

test/unit/lexer_unit_test.rb

@@ -134,6 +134,6 @@ class LexerUnitTest < Minitest::Test
   private
 
   def tokenize(input)
-    Lexer.tokenize(input, StringScanner.new(""))
+    Lexer.tokenize(StringScanner.new(input))
   end
 end

test/unit/parser_unit_test.rb

@@ -85,6 +85,6 @@ class ParserUnitTest < Minitest::Test
   private
 
   def new_parser(str)
-    Parser.new(str, StringScanner.new(""))
+    Parser.new(StringScanner.new(str))
   end
 end