MLton 20210117

# MLtonExn

    signature MLTON_EXN =
       sig
          val addExnMessager: (exn -> string option) -> unit
          val history: exn -> string list

          val defaultTopLevelHandler: exn -> 'a
          val getTopLevelHandler: unit -> (exn -> unit)
          val setTopLevelHandler: (exn -> unit) -> unit
          val topLevelHandler: exn -> 'a
       end

- addExnMessager f

  adds f as a pretty-printer to be used by General.exnMessage for converting exceptions to strings. Messagers are tried in order from most recently added to least recently added.

- history e

  returns call stack at the point that e was first raised. Each element of the list is a file position. The elements are in reverse chronological order, i.e. the function called last is at the front of the list.

  history e will return [] unless the program is compiled with -const 'Exn.keepHistory true'.

- defaultTopLevelHandler e

  function that behaves as the default top level handler; that is, print out the unhandled exception message for e and exit.

- getTopLevelHandler ()

  get the top level handler.

- setTopLevelHandler f

  set the top level handler to the function f. The function f should not raise an exception or return normally.

- topLevelHandler e

  behaves as if the top level handler received the exception e.