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;
; It is possible to create an anonymous function.
(lambda (x) (+ x 1))
;
; This is fairly useless unless you call it.
((lambda (x) (+ x 1)) 17)
; Which is a very verbose version of (+ 17 1)
;
; (mapcar f list) applies the function to each member of the list to give
; a new list.
(mapcar 'abs '(4 5 -3 -11 4))
;
; Mapcar can also work with multiple lists. The number of lists must equal
; the arity of the function.
(mapcar '+ '(4 17 7) '(8 -5 21))
;
; Anonymous functions can be used with mapcar.
(mapcar (lambda (x) (+ x 1)) '(4 18 5 11 8))
(mapcar (lambda (x y) (+ (* x x) (* y y))) '(4 9 7 16) '(1 8 2 1))
;
; The reduce function will combine all the members of a list to
; form a result value which is the combination of these. Here's
; a way to sum a list or take a product:
(reduce '+ '(4 9 2 1)) ; Equiv to (+ (+ (+ 4 9) 2) 1)
(reduce '* '(4 9 2 1)) ; Equiv to (* (* (* 4 9) 2) 1)
;
; Here's a brain-damaged, .. er.., interesting way to find the length of a
; list.
(defun oddlen (lis) (reduce '+ (mapcar (lambda (x) 1) lis)))
(oddlen '(this is a list))
;
; This function selects the members of the list which satisfy the predicate.
; It is inconceivable that Common Lisp does not provide this somewhere as
; a standard function, but I cannot for the life of me find it. It's probably
; called something obvious like idaho.
(defun select (f? lis)
(cond
((null lis) ())
((funcall f? (car lis)) (cons (car lis) (select f? (cdr lis))))
(t (select f? (cdr lis)))
)
)
(select (lambda (x) (> x 10)) '(4 14 10 23 4 9 18))
;
; Here's a version of select sort on a lisp list.
(defun select_sort (lis)
(if (or (null lis) (null (cdr lis)))
lis
(let*
(
(themax (reduce 'max lis))
(maxes (select (lambda (x) (= x themax)) lis))
(others (select (lambda (x) (/= x themax)) lis))
)
(append maxes (select_sort others))
)
)
)
(select_sort '(4 9 18 4 45 18 4 12 4 198 15 8))
(select_sort '(22))