Should we add scm_to_pointer, or just use SCM_POINTER_VALUE?

[Mark H Weaver]

I was chatting with rcfox on #guile, who needed to extract the C pointer
from a SCM pointer object, from C code.  In this case, it was a C
callback created using 'procedure->pointer'.

I tried to discourage him from using SCM_POINTER_VALUE, because it's
undocumented and will embed internal details of our representation into
his binary, but he was undeterred :)

Should we add 'scm_to_pointer'?  For most other accessors, the trend
seems to be to discourage use of C macros and move people over to C
functions instead.  With that in mind, it seems inconsistent to have
people using SCM_POINTER_VALUE for lack of a C function to do this job.

What do you think?

    Mark