diff --git a/src/structs.h b/src/structs.h
index 3efd6ab..d429100 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3263,6 +3263,22 @@
 } context_sha256_T;
 
 /*
+ * types for expressions.
+ */
+typedef enum
+{
+    TYPE_UNKNOWN = 0
+    , TYPE_EQUAL	/* == */
+    , TYPE_NEQUAL	/* != */
+    , TYPE_GREATER	/* >  */
+    , TYPE_GEQUAL	/* >= */
+    , TYPE_SMALLER	/* <  */
+    , TYPE_SEQUAL	/* <= */
+    , TYPE_MATCH	/* =~ */
+    , TYPE_NOMATCH	/* !~ */
+} exptype_T;
+
+/*
  * Structure used for reading in json_decode().
  */
 struct js_reader