If one of these procedures is called with no arguments (or with
setting == SCM_UNDEFINED in C code), it returns a list describing
the current setting of the read, eval, print, debug or evaluator traps
options respectively. The setting of a boolean option is indicated
simply by the presence or absence of the option symbol in the list. The
setting of a non-boolean option is indicated by the presence of the
option symbol immediately followed by the option's current value.
If called with a list argument, these procedures interpret the list as
an option setting and modify the relevant options accordingly. [FIXME
--- this glosses over a lot of details!]
If called with any other argument, such as 'help, these
procedures return a list of entries like (OPTION-SYMBOL
DEFAULT-VALUE DOC-STRING), with each entry giving the
default value and documentation for each option symbol in the relevant
set of options.
