librep

Matthew Kirkwood writes:
|Unfortunately, my Lisp isn't very good, so I'm causing
|a lot of errors which are hard to track down because
|I can't test without calls back into my C functions.

the best way to track errors is to do something like:

(setq backtrace-on-error '(bad-arg missing-arg void-value invalid-function))

plus any other errors you're getting. This should cause a lisp
backtrace to be printed

another option is to replace backtrace-on-error by debug-on-error to
cause errors to enter the debugger (it's very basic)

|
|Looking around the headers, I see a Qerror_message
|but I can't get anything but the empty string from it.

Qerror_message is a symbol used to associate descriptions with errors,
it's not very useful

when a function returns rep_NULL, the variable rep_throw_value will
point to a cons cell, the car defines the type of exception (Qerror for
an error), the cdr is data associated with the exception (a list for
errors)

the usual behaviour when receiving a null result is to abort and return
null to the caller. If the current function is the ``top level'' of the
program, then it can call rep_handle_input_exception to do something
with the error (i.e. print it) (see librep/src/main.c for this
function)

	John