Add support for leaflist

Change-Id: Idcb529f85240a32e84d82934c81fcf0c3451f94e
diff --git a/src/ast_values.cpp b/src/ast_values.cpp
index a381c1a..c3f2ce7 100644
--- a/src/ast_values.cpp
+++ b/src/ast_values.cpp
@@ -99,6 +99,8 @@
         return "(presence container)";
     case SpecialValue::List:
         return "(list)";
+    case SpecialValue::LeafList:
+        return "(leaflist)";
     }
 
     __builtin_unreachable();