Handle shifting states after reducing

spec/propane_spec.rb

@@ -74,10 +74,13 @@ EOF
     write_grammar <<EOF
 token a
 token b
+drop \\s+
 Start -> a R1;
 Start -> b R1;
 R1 -> b;
 EOF
     build_parser
+    compile("spec/test_d_lexer2.d")
+    run
   end
 end

spec/test_d_lexer2.d

@@ -0,0 +1,22 @@
+import testparser;
+import std.stdio;
+
+int main()
+{
+    return 0;
+}
+
+unittest
+{
+    string input = "a";
+    auto parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    assert(parser.parse() == false);
+
+    input = "a b";
+    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    assert(parser.parse() == true);
+
+    input = "bb";
+    parser = new Testparser.Parser(cast(const(ubyte) *)input.ptr, input.length);
+    assert(parser.parse() == true);
+}