Unlike many programs compiled from C or FORTRAN code, the
code, being written in an interpreted language, almost never crashes
by returning to the operating system prompt. What usually happens is
that execution stops at the offending line in the script and an error
message is printed. At this point, the fearless user can print values of
variables, enter IDL commands, all within the current context, in order
to investigate the causes of the crash. To resume the
session
by backing out of the procedure, it is best to return right away to the
main level by typing retall.