Availability:C-language interface function
int PL_skip_list(term_t
+list, term_t -tail, size_t *len)This is a multi-purpose function to deal with lists. It allows for
finding the length of a list, checking whether something is a list, etc.
The reference tail is set to point to the end of the list,
len is filled with the number of list-cells skipped, and the
return value indicates the status of the list:
- PL_LIST
- The list is a‘proper’list: one that ends in the list
terminator constant and tail is filled with the terminator
constant.
- PL_PARTIAL_LIST
- The list is a‘partial’list: one that ends in a variable and
tail is a reference to this variable.
- PL_CYCLIC_TERM
- The list is cyclic (e.g. X = [a|X]). tail points to an
arbitrary cell of the list and len is at most twice the cycle
length of the list.
- PL_NOT_A_LIST
- The term list is not a list at all. tail is bound
to the non-list term and len is set to the number of
list-cells skipped.
It is allowed to pass 0 for tail and NULL for len.