If an error occurs during the evaluation of U, the value of NUMBER
from the ERROR call is returned as the value of ERRORSET. In
addition, if the value of MSGP is non-NIL, the MESSAGE from
the ERROR call is displayed upon both the standard output device
and the currently selected output device unless the standard output
device is not open. The message appears prefixed with 5 asterisks.
The MESSAGE list is displayed without top level parentheses. The
MESSAGE from the ERROR call will be available in the global
variable EMSG!*. The exact format of error messages generated
by Standard LISP functions described in this document are not
fixed and should not be relied upon to be in any particular form.
Likewise, error numbers generated by Standard LISP functions are
If no error occurs during the evaluation of U, the value of (LIST
(EVAL U)) is returned.
If an error has been signaled and the value of TR is non-NIL a
traceback sequence will be initiated on the selected output device.
The traceback will display information such as unbindings of FLUID
variables, argument lists and so on in an implementation dependent