Node:Unpacking the SCM type, Previous:Signalling Type Errors, Up:How Guile does it
The previous sections have explained how SCM values can refer to
immediate and non-immediate Scheme objects. For immediate objects, the
complete object value is stored in the SCM word itself, while for
non-immediates, the SCM word contains a pointer to a heap cell,
and further information about the object in question is stored in that
cell. This section describes how the SCM type is actually
represented and used at the C level.
In fact, there are two basic C data types to represent objects in Guile:
| SCM | Data type |
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 | Data type |
scm_t_bits is an 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.
|