(mapcar #'1+ '(1 2 3))
;; => (2 3 4)
mapcar is a higher order function since it takes a function and applies it to each element in the list
(function 1+)
;; => #<FUNCTION 1+>
#'1+
;; => #<FUNCTION 1+>
- Here we can see how to reference functions differently.
- "Sharp quote" (
#') is how you can reference a function
- The function,
function is the equivalent of sharp quote
(defun plus-one (a) (+ 1 a))
;; => PLUS-ONE
(mapcar (function plus-one) '(1 2 3))
;; => (2 3 4)
- Just like calling standard library functions you can also use your own.
(mapcar #'(lambda (a) (+ a 1)) '(1 2 3))
;; => (2 3 4)
lambda allows you to define an anonymous (i.e. unnamed) function inline.- It is valid to provide an unquoted lambda but this is perhaps inadvisable.
(defun my-map (f list)
(cond
((null list) nil)
(t (cons (funcall f (first list))
(my-map f (rest list))))))
;; => MY-MAP
(my-map (lambda (a) (+ a 1)) '(1 2 3))
;; => (2 3 4)
- When defining our own higher order functions we need to use
funcall. This
is because the first argument passed into our function is in the "value namespace",
which means we can't just call it as if it's a function. What funcall does is let
us "lift" the function from the value namespace into the function namespace.