diff --git a/lib/rpl/interpreter.rb b/lib/rpl/interpreter.rb
index f693143..fb3096a 100644
--- a/lib/rpl/interpreter.rb
+++ b/lib/rpl/interpreter.rb
@@ -197,7 +197,7 @@ class Interpreter
 
       "#{prefix}#{suffix}"
     when :list
-      "[#{elt[:value].map { |e| stringify( e ) }.join(', ')}]"
+      "{ #{elt[:value].map { |e| stringify( e ) }.join(' ')} }"
     when :program
       "« #{elt[:value]} »"
     when :string