1 files changed, 30 insertions, 0 deletions
diff --git a/ql/ast/checkers/reference_checker.py b/ql/ast/checkers/reference_checker.py
new file mode 100644
index 0000000..71407c3
--- /dev/null
+++ b/ql/ast/checkers/reference_checker.py
@@ -0,0 +1,30 @@
+class ReferenceChecker:
+    def __init__(self, table):
+        self.__errors = []
+        self.__check_references(table, [], [])
+
+    @property
+    def errors(self):
+        return self.__errors
+
+    def __check_references(self, table, known_types, unknown_types):
+        (local_known_types, local_unknown_types) = self.__split_known_unknown_types(table)
+        known_types += local_known_types
+        unknown_types += local_unknown_types
+
+        self.__identifier_seen(known_types, unknown_types)
+
+        if table['children']:
+            for child_scope in table['children']:
+                self.__check_references(child_scope, known_types, unknown_types)
+
+    @staticmethod
+    def __split_known_unknown_types(table):
+        known_types = [row['name'] for row in table['content'] if row['type']]
+        unknown_types = [(row['name'], row['line']) for row in table['content'] if not (row['type'])]
+        return known_types, unknown_types
+
+    def __identifier_seen(self, known_types, unknown_types):
+        for (identifier, line) in unknown_types:
+            if not (identifier in known_types):
+                self.__errors.append('Identifier \"{}\" at line {} is unknown'.format(identifier, line))