keyword expressions

and smaller new harness

lib/parser/keywords.citrus

@@ -7,16 +7,22 @@ grammar Keywords
   rule keyword_do       'do'     space? end
   rule keyword_else     'else'   space?  end
   rule keyword_end      'end'    space?  end
-  rule keyword_false    'false'  space? end
   rule keyword_if       'if'     space?  end
   rule keyword_rescue   'rescue' space? end
   rule keyword_return   'return' space? end
   rule keyword_module   'module' space?  end
-  rule keyword_nil      'nil'    space? end
   rule keyword_unless   'unless' space? end
   rule keyword_until    'until'  space? end
   rule keyword_while    'while'  space? end
 
+  rule keyword_nil
+    ('nil'    space? ){ Ast::NilExpression.new }
+  end
+
+  rule keyword_false
+    ('false'  space?) { Ast::FalseExpression.new }
+  end
+
   rule keyword_true
     ('true'   space?) { Ast::TrueExpression.new }
   end
@@ -28,4 +34,9 @@ grammar Keywords
                    'unless' |  'until' |  'while') space?
   end
 
+  rule keyword_expression
+    keyword_true | keyword_false | keyword_nil
+  end
+
+  root  keyword_expression
 end