diff --git a/generator/js_of_ast.ml b/generator/js_of_ast.ml
index 7ecdb835bd0f56456f9cff114f3d0aaed4a62975..10a96d264eda974c987aa55f20ea001df890d93f 100644
--- a/generator/js_of_ast.ml
+++ b/generator/js_of_ast.ml
@@ -27,6 +27,7 @@ let show_list sep l =
 
 let is_sbool x = List.mem x ["true" ; "false"]
 
+(* Given an expression, check whether it is a primitive type or a constructed type *)
 let exp_type_is_constant exp =
   List.exists (Ctype.matches exp.exp_env exp.exp_type)
   [Predef.type_bool; Predef.type_int; Predef.type_char; Predef.type_string; Predef.type_float]