diff --git a/bin/sixtypical b/bin/sixtypical
index 7f98e03..f16ffac 100755
--- a/bin/sixtypical
+++ b/bin/sixtypical
@@ -51,37 +51,8 @@ def process_input_files(filenames, options):
             sys.stdout.write("\n")
 
     if options.dump_callgraph:
-        graph = {}
-
-        from sixtypical.model import RoutineType, VectorType
-
-        def find_routines_matching_vector_type(program, type_):
-            return []  # dummy
-
-        for routine in program.routines:
-            potentially_calls = []
-            for (called_routine, called_routine_type) in routine.called_routines:
-                if isinstance(called_routine_type, RoutineType):
-                    potentially_calls.append(called_routine.name)
-                elif isinstance(called_routine_type, VectorType):
-                    for potentially_called in find_routines_matching_vector_type(program, called_routine_type):
-                        potentially_calls.append(potentially_called.name)
-                else:
-                    raise NotImplementedError
-            graph[routine.name] = {
-                'potentially-calls': potentially_calls,
-            }
-
-        # Reflexive closure
-
-        for routine in program.routines:
-            potentially_called_by = []
-            for (name, node) in graph.items():
-                potential_calls = node['potentially-calls']
-                if routine.name in potential_calls:
-                    potentially_called_by.append(name)
-            graph[routine.name]['potentially-called-by'] = potentially_called_by
-
+        from sixtypical.callgraph import construct_callgraph
+        graph = construct_callgraph(program)
         sys.stdout.write(json.dumps(graph, indent=4, sort_keys=True, separators=(',', ':')))
 
     compilation_roster = None
diff --git a/src/sixtypical/callgraph.py b/src/sixtypical/callgraph.py
new file mode 100644
index 0000000..d7a9773
--- /dev/null
+++ b/src/sixtypical/callgraph.py
@@ -0,0 +1,35 @@
+from sixtypical.model import RoutineType, VectorType
+
+
+def find_routines_matching_vector_type(program, type_):
+    return []  # dummy
+
+
+def construct_callgraph(program):
+    graph = {}
+
+    for routine in program.routines:
+        potentially_calls = []
+        for (called_routine, called_routine_type) in routine.called_routines:
+            if isinstance(called_routine_type, RoutineType):
+                potentially_calls.append(called_routine.name)
+            elif isinstance(called_routine_type, VectorType):
+                for potentially_called in find_routines_matching_vector_type(program, called_routine_type):
+                    potentially_calls.append(potentially_called.name)
+            else:
+                raise NotImplementedError
+        graph[routine.name] = {
+            'potentially-calls': potentially_calls,
+        }
+
+    # Reflexive closure
+
+    for routine in program.routines:
+        potentially_called_by = []
+        for (name, node) in graph.items():
+            potential_calls = node['potentially-calls']
+            if routine.name in potential_calls:
+                potentially_called_by.append(name)
+        graph[routine.name]['potentially-called-by'] = potentially_called_by
+
+    return graph