diff --git a/src/parser/parser.cc b/src/parser/parser.cc
index b38fb0c..74b0b50 100644
--- a/src/parser/parser.cc
+++ b/src/parser/parser.cc
@@ -6,6 +6,8 @@
 #include <unistd.h>
 #include <stdbool.h>
 
+std::unordered_set<std::string> type_names;
+
 extern FILE * yyin;
 
 static const char * input_fname;
@@ -192,3 +194,8 @@ void handle_parse_error(const char * str, const YYLTYPE * yylloc)
             yylloc->last_column);
     display_error_source(yylloc->last_line, yylloc->last_column);
 }
+
+void observe_type_name(const std::string & type_name)
+{
+    type_names.insert(type_name);
+}
diff --git a/src/parser/parser.h b/src/parser/parser.h
index 2526f0d..7666566 100644
--- a/src/parser/parser.h
+++ b/src/parser/parser.h
@@ -3,10 +3,15 @@
 
 #include "Node.h"
 #include "parser.tab.hh"
+#include <unordered_set>
+#include <string>
 
 #define YYSTYPE Node *
 
+extern std::unordered_set<std::string> type_names;
+
 void parse(const char * filename);
 void handle_parse_error(const char * str, const YYLTYPE * yylloc);
+void observe_type_name(const std::string & type_name);
 
 #endif