BREAK():{Error,return-value}
----------------------------
This is a Read-Eval-Print loop, similar to the top level loop, except
that the following IDs at the top level cause functions to be called
rather than being evaluated:
? Print this message, listing active Break IDs
T Print stack backtrace
Q Exit break loop back to ErrorSet
A Abort to top level, i.e. restart PSL
C Return last value to the ContinuableError call
R Reevaluate ErrorForm!* and return
M Display ErrorForm!* as the "message"
E Invoke a simple structure editor on ErrorForm!*
(For more information do Help Editor.)
I Show a trace of any interpreted functions
See the manual for details on the Backtrace, and how ErrorForm!* is
set. The Break Loop attempts to use the same TopLoopRead!* etc, as
the calling top loop, just expanding the PromptString!*.