]> Hello, I have a not-so-easy-to-reproduce case in which ===== let tbl = Hashtbl.create 7 let f x = Hashtbl.find tbl x let g b = Marshal.to_string (fun _ -> f b) [ Marshal.Closures ] ... let _ = g ... ===== may raise the exception ===== Fatal error: exception Invalid_argument("output_value: abstract value (Abstract)"). ===== If I wrote the above code like below, all is fine: ===== let tbl = Hashtbl.create 7 let f x = Hashtbl.find tbl x;; let g b = let y = f b in Marshal.to_string (fun _ -> y) [ Marshal.Closures ] ... let _ = g ... ===== After debugging, that is the marshalling of the field 1 of the closure (the environment?) which raises this exception. Can someone confirm that such a behaviour is possible whenever the environment contains a value tagged as abstract? Or in any other cases? If that is a known behaviour for Marshal.to_string, maybe it could be properly documented? Best regards, Julien Signoles