www.delorie.com/gnu/docs/guile/guile_219.html   search  
 
Buy GNU books!


Guile Reference Manual

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

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.


  webmaster     delorie software   privacy  
  Copyright 2003   by The Free Software Foundation     Updated Jun 2003