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(in-package :araneida)
;; (foldr (lambda (x y) (string-append x "; " y)) '(" 3" "2" "1"))
;; => 3; 2; 1
;; (foldr (lambda (x y) (string-append "(" x "; " y ")")) '(" 3" "2" "1"))
;; => ( 3; (2; 1))
(defun foldr (func list)
"Fold FUNC over LIST, starting at the right-hand end"
(cond ((null (cdr list))
(car list))
(t
(funcall func (car list) (foldr func (cdr list) )))))
;; (foldl (lambda (x y) (string-append x "; " y)) '(" 3" "2" "1"))
;; => 3; 2; 1
;; (foldl (lambda (x y) (string-append "(" x "; " y ")")) '(" 3" "2" "1"))
;; => (( 3; 2); 1)
(defun foldl (f lst) (foldr (lambda (y x) (funcall f x y)) (reverse lst)))
(defun join (delimiter elements)
"Returns a new string consisting of ELEMENTS with DELIMITERs between them. Elements are converted to strings as if by PRINC-TO-STRING"
(with-output-to-string (o)
(loop for front on elements
if (> (length front) 1)
do (progn (princ (car front) o) (princ delimiter o))
else
do (princ (car front) o))))
(defun choose-best (list test &key (key 'identity))
"Effectively equivalent to (elt (sort list test :key key) 0) but potentially faster"
(loop for el in list
for so-far = el then (if (funcall test (funcall key el)
(funcall key so-far))
el
so-far)
finally (return so-far)))
#|
(choose-best '(#\1 #\2 #\1 #\8 #\3 #\0) #'> :key #'char-code) => 8
|#
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