Guile Reference Manual
22.2.2 List Predicates
Often it is useful to test whether a given Scheme object is a list or
not. List-processing procedures could use this information to test
whether their input is valid, or they could do different things
depending on the datatype of their arguments.
- Scheme Procedure: list? x
-
- C Function: scm_list_p (x)
- Return
#t iff x is a proper list, else #f.
The predicate null? is often used in list-processing code to
tell whether a given list has run out of elements. That is, a loop
somehow deals with the elements of a list until the list satisfies
null?. Then, the algorithm terminates.
- Scheme Procedure: null? x
-
- C Function: scm_null_p (x)
- Return
#t iff x is the empty list, else #f.
