1 files changed, 15 insertions, 2 deletions

diff --git a/vm.d b/vm.d
index fbf874c..c5de28c 100644
--- a/vm.d
+++ b/vm.d
@@ -192,6 +192,14 @@ class VM {
         return value.as.seq;
     }
 
+    List asList(Value value) {
+        return cast(List)value.as.seq;
+    }
+
+    String asNebString(Value value) {
+        return cast(String)value.as.seq;
+    }
+
     double asNumber(Value value) {
         return value.as.number;
     }
@@ -491,10 +499,15 @@ class VM {
                     this.pushA(makeBooleanValue(areValuesEqual(a, b)));
                     break;
                 case OpCode.OP_CONCAT:
-                    Seq b = asSeq(this.popA());
-                    Seq a = asSeq(this.popA());
+                    String b = asNebString(this.popA());
+                    String a = asNebString(this.popA());
                     this.pushA(makeSeqValue(a.concat(b)));
                     break;
+                case OpCode.OP_APPEND:
+                    Value b = this.popA();
+                    List a = asList(this.popA());
+                    this.pushA(makeSeqValue(a.append(b)));
+                    break;
                 case OpCode.OP_GREATER:
                     Value b = this.popA();
                     Value a = this.popA();