diff --git a/core/stl.c b/core/stl.c
index c5563f30..e3092f09 100644
--- a/core/stl.c
+++ b/core/stl.c
@@ -23,6 +23,20 @@
 #include <dst/dst.h>
 #include <dst/dststl.h>
 
+int dst_stl_push(int32_t argn, Dst *argv, Dst *ret) {
+    if (argn != 2) {
+        *ret = dst_cstringv("expected 2 arguments");
+        return 1;
+    }
+    if (!dst_checktype(argv[0], DST_ARRAY)) {
+        *ret = dst_cstringv("expected array");
+        return 1;
+    }
+    dst_array_push(dst_unwrap_array(argv[0]), argv[1]);
+    *ret = argv[0];
+    return 0;
+}
+
 int dst_stl_parse(int32_t argn, Dst *argv, Dst *ret) {
     const uint8_t *src;
     int32_t len;
@@ -385,6 +399,7 @@ DST_DEFINE_COMPARATOR(notdescending, > 0)
 DST_DEFINE_COMPARATOR(notascending, < 0)
 
 static DstReg stl[] = {
+    {"push", dst_stl_push},
     {"load-native", dst_load_native},
     {"parse", dst_stl_parse},
     {"compile", dst_stl_compile},
diff --git a/dsttest/suite0.dst b/dsttest/suite0.dst
index 0e1777ba..5ff6d491 100644
--- a/dsttest/suite0.dst
+++ b/dsttest/suite0.dst
@@ -180,8 +180,7 @@
 
 # Merge sort
 
-(def empty? (fn [xs] (= 0 (length xs))))
-
+# Impertiave merge sort merge
 (def merge (fn [xs ys] 
     (def ret [])
     (def xlen (length xs))
@@ -207,6 +206,11 @@
       (varset! j (+ j 1)))    
     ret))
 
+(assert (apply <= (merge [1 3 5] [2 4 6])) "merge sort merge 1")
+(assert (apply <= (merge [1 2 3] [4 5 6])) "merge sort merge 2")
+(assert (apply <= (merge [1 3 5] [2 4 6 6 6 9])) "merge sort merge 3")
+(assert (apply <= (merge '(1 3 5) [2 4 6 6 6 9])) "merge sort merge 4")
+
 # Gensym tests
 
 (assert (not= (gensym) (gensym)) "two gensyms not equal")