Warning: This is the manual of the legacy Guile 2.0 series. You may want to read the manual of the current stable series instead.
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A Scheme object of type SCM
that does not fulfill the
SCM_IMP
predicate holds an encoded reference to a heap cell.
This reference can be decoded to a C pointer to a heap cell using the
SCM2PTR
macro. The encoding of a pointer to a heap cell into a
SCM
value is done using the PTR2SCM
macro.
Extract and return the heap cell pointer from a non-immediate SCM
object x.
Return a SCM
value that encodes a reference to the heap cell
pointer x.
Note that it is also possible to transform a non-immediate SCM
value by using SCM_UNPACK
into a scm_t_bits
variable.
However, the result of SCM_UNPACK
may not be used as a pointer to
a scm_t_cell
: only SCM2PTR
is guaranteed to transform a
SCM
object into a valid pointer to a heap cell. Also, it is not
allowed to apply PTR2SCM
to anything that is not a valid pointer
to a heap cell.
Summary:
SCM2PTR
on SCM
values for which SCM_IMP
is
false!
(scm_t_cell *) SCM_UNPACK (x)
! Use SCM2PTR
(x)
instead!
PTR2SCM
for anything but a cell pointer!