A mapping function applies a function to each of a collection of
objects. Librep currently has two mapping functions,
Each element of list is individually applied to the function function. The values returned are made into a new list which is returned.
The function must accept a single argument value.
(mapcar 1+ '(1 2 3 4 5)) ⇒ (2 3 4 5 6)
mapcar except that the values returned when each
element is applied to the function function are discarded. The
value returned is undefined.
This function is generally used where the side effects of calling the function are the important thing, not the results. It is often the most efficient way of traversing all items in a list, for example:
(mapc (lambda (x) (print x standard-error)) list)
The two following functions are also mapping functions of a sort. They
are variants of the
delete function (see Modifying Lists)
and use predicate functions to classify the elements of the list which
are to be deleted.
This function is a variant of the
delete function. Instead of
comparing each element of list with a specified object, each
element of list is applied to the predicate function
predicate. If it returns true then the
element is destructively removed from list.
(delete-if stringp '(1 "foo" 2 "bar" 3 "baz")) ⇒ (1 2 3)
This function does the inverse of
delete-if. It applies
predicate to each element of list, if it returns false
then the element is destructively removed from the list.
(delete-if-not stringp '(1 "foo" 2 "bar" 3 "baz")) ⇒ ("foo" "bar" "baz")
delete-if-not respectively, but
returns a new copy, instead of destructively. Defined in
filter function is similar to
that the original list isn’t modified, a new list is created.
Return a new list, consisting of the elements in list which the function predicate returns true when applied to. This function is equivalent to:
(mapcar nconc (mapcar (lambda (x) (and (predicate x) (list x))) list))