gadt_issue.ml

type (_, _) typ =
  (* ... other definitions *)
  | DynTyp : 'ctx dyn -> ('ctx, 'ctx dyn) typ
and 'ctx dyn =
  Dyn : ('ctx, 'src) typ * 'src -> 'ctx dyn

let rec typ_to_string : type src. ('ctx, src) typ -> 'ctx -> src -> string =
  fun typ ctx src ->
    match typ with
    (* ... other match cases *)
    | DynTyp (Dyn (typ', src')) -> typ_to_string typ' ctx src'

Error: This pattern matches values of type ($'ctx, $'ctx dyn) typ
       The type constructor $'ctx would escape its scope