diff --git a/src/runtime/c/pgf/evaluator.h b/src/runtime/c/pgf/evaluator.h
new file mode 100644
index 000000000..b2cffd167
--- /dev/null
+++ b/src/runtime/c/pgf/evaluator.h
@@ -0,0 +1,32 @@
+#ifndef PGF_EVALUATOR_H_
+#define PGF_EVALUATOR_H_
+
+struct PgfEvalState {
+	PgfPGF* pgf;
+	GuPool* pool;
+	GuExn* err;
+	GuBuf* stack;
+};
+
+typedef struct PgfClosure PgfClosure;
+typedef struct PgfEvalState PgfEvalState;
+
+typedef PgfClosure* (*PgfFunction)(PgfEvalState* state, PgfClosure* val);
+
+struct PgfClosure {
+	PgfFunction code;
+};
+
+typedef struct {
+	PgfClosure header;
+	PgfAbsFun* absfun;
+	PgfClosure* args[];
+} PgfValue;
+
+PgfClosure*
+pgf_evaluate_value(PgfEvalState* state, PgfClosure* closure);
+
+void
+pgf_evaluate_save_variables(PgfEvalState* state, PgfValue* val);
+
+#endif