9.2.5.6 Accessing Cell Entries

For a non-immediate Scheme object x, the object type can be determined by reading the cell type entry using the SCM_CELL_TYPE macro. For each different type of cell it is known which cell entries hold Scheme objects and which cell entries hold raw C data. To access the different cell entries appropriately, the following macros are provided.

Macro: scm_t_bits SCM_CELL_WORD (SCM x, unsigned int n)

Deliver the cell entry n of the heap cell referenced by the non-immediate Scheme object x as raw data. It is illegal, to access cell entries that hold Scheme objects by using these macros. For convenience, the following macros are also provided.

• SCM_CELL_WORD_0 (x) ⇒ SCM_CELL_WORD (x, 0)
• SCM_CELL_WORD_1 (x) ⇒ SCM_CELL_WORD (x, 1)
• …
• SCM_CELL_WORD_n (x) ⇒ SCM_CELL_WORD (x, n)

Macro: SCM SCM_CELL_OBJECT (SCM x, unsigned int n)

Deliver the cell entry n of the heap cell referenced by the non-immediate Scheme object x as a Scheme object. It is illegal, to access cell entries that do not hold Scheme objects by using these macros. For convenience, the following macros are also provided.

• SCM_CELL_OBJECT_0 (x) ⇒ SCM_CELL_OBJECT (x, 0)
• SCM_CELL_OBJECT_1 (x) ⇒ SCM_CELL_OBJECT (x, 1)
• …
• SCM_CELL_OBJECT_n (x) ⇒ SCM_CELL_OBJECT (x, n)

Macro: void SCM_SET_CELL_WORD (SCM x, unsigned int n, scm_t_bits w)

Write the raw C value w into entry number n of the heap cell referenced by the non-immediate Scheme value x. Values that are written into cells this way may only be read from the cells using the SCM_CELL_WORD macros or, in case cell entry 0 is written, using the SCM_CELL_TYPE macro. For the special case of cell entry 0 it has to be made sure that w contains a cell type information which does not describe a Scheme object. For convenience, the following macros are also provided.

• SCM_SET_CELL_WORD_0 (x, w) ⇒ SCM_SET_CELL_WORD (x, 0, w)
• SCM_SET_CELL_WORD_1 (x, w) ⇒ SCM_SET_CELL_WORD (x, 1, w)
• …
• SCM_SET_CELL_WORD_n (x, w) ⇒ SCM_SET_CELL_WORD (x, n, w)

Macro: void SCM_SET_CELL_OBJECT (SCM x, unsigned int n, SCM o)

Write the Scheme object o into entry number n of the heap cell referenced by the non-immediate Scheme value x. Values that are written into cells this way may only be read from the cells using the SCM_CELL_OBJECT macros or, in case cell entry 0 is written, using the SCM_CELL_TYPE macro. For the special case of cell entry 0 the writing of a Scheme object into this cell is only allowed if the cell forms a Scheme pair. For convenience, the following macros are also provided.

• SCM_SET_CELL_OBJECT_0 (x, o) ⇒ SCM_SET_CELL_OBJECT (x, 0, o)
• SCM_SET_CELL_OBJECT_1 (x, o) ⇒ SCM_SET_CELL_OBJECT (x, 1, o)
• …
• SCM_SET_CELL_OBJECT_n (x, o) ⇒ SCM_SET_CELL_OBJECT (x, n, o)

Summary:

• For a non-immediate Scheme object x of unknown type, get the type information by using SCM_CELL_TYPE (x).
• As soon as the cell type information is available, only use the appropriate access methods to read and write data to the different cell entries.

This document was generated on April 20, 2013 using texi2html 5.0.