Re: Progress on using FvwmButtons (and some questions)

[Greg Badros <gjb@cs.washington.edu>]

<For the guile list that I'm now cc'ing, this is a thread from
scwm-discuss about avoiding bugs where a long/int is used where an SCM
was meant to be used -- inspired by a hard-to-find bug in Scwm due to
SCM being typedefed to long>

Maciej Stachowiak <mstachow@mit.edu> writes:

> Not all SCMs are actually pointers, characters and integers up to 30
> bits are stored directly in that word, with a type tag. One could come
> up with an assertion based on the possible values of the type tags,
> but this would be pretty complicated.

Which is why we have abstractions like macros and functions.  From a
quick look at tags.h, it looks as though the valid SCM values are sparse
enough and well-defined enough that perhaps a macro for validating SCMs
could be written.  Then asserting the validity of all SCMs at function
calls in a debug build might help catch some errors dynamically.
Obviously I'd prefer a solution that got us this statically, but it
sounds like that would require more pervasive changes to guile.

Greg