Guile represents all Scheme values with the single C type SCM.
For an introduction to this topic, See Dynamic Types.
SCM is the user level abstract C type that is used to represent
all of Guile’s Scheme objects, no matter what the Scheme object type is.
No C operation except assignment is guaranteed to work with variables of
type SCM, so you should only use macros and functions to work
with SCM values. Values are converted between C data types and
the SCM type with utility functions and macros.
scm_t_bits is an unsigned integral data type that is guaranteed
to be large enough to hold all information that is required to
represent any Scheme object. While this data type is mostly used to
implement Guile’s internals, the use of this type is also necessary to
write certain kinds of extensions to Guile.
This is a signed integral type of the same size as scm_t_bits.
scm_t_bits SCM_UNPACK (SCM x) ¶Transforms the SCM value x into its representation as an
integral type. Only after applying SCM_UNPACK it is possible to
access the bits and contents of the SCM value.
SCM SCM_PACK (scm_t_bits x) ¶Takes a valid integral representation of a Scheme object and transforms
it into its representation as a SCM value.