If one of these procedures is called with no arguments (or with
setting == SCM_UNDEFINEDin 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.