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GNU Info (elisp)List-related PredicatesPredicates on Lists =================== The following predicates test whether a Lisp object is an atom, is a cons cell or is a list, or whether it is the distinguished object `nil'. (Many of these predicates can be defined in terms of the others, but they are used so often that it is worth having all of them.) - Function: consp object This function returns `t' if OBJECT is a cons cell, `nil' otherwise. `nil' is not a cons cell, although it _is_ a list. - Function: atom object This function returns `t' if OBJECT is an atom, `nil' otherwise. All objects except cons cells are atoms. The symbol `nil' is an atom and is also a list; it is the only Lisp object that is both. (atom OBJECT) == (not (consp OBJECT)) - Function: listp object This function returns `t' if OBJECT is a cons cell or `nil'. Otherwise, it returns `nil'. (listp '(1)) => t (listp '()) => t - Function: nlistp object This function is the opposite of `listp': it returns `t' if OBJECT is not a list. Otherwise, it returns `nil'. (listp OBJECT) == (not (nlistp OBJECT)) - Function: null object This function returns `t' if OBJECT is `nil', and returns `nil' otherwise. This function is identical to `not', but as a matter of clarity we use `null' when OBJECT is considered a list and `not' when it is considered a truth value (see `not' in Note: Combining Conditions). (null '(1)) => nil (null '()) => t automatically generated by info2www version 1.2.2.9 |