30 - Functional#
str-split#
(define (str-split str ch)
(let ((len (string-length str)))
(letrec
((split
(lambda (a b)
(cond
((>= b len) (if (= a b) '() (cons (substring str a b) '())))
((char=? ch (string-ref str b)) (if (= a b)
(split (+ 1 a) (+ 1 b))
(cons (substring str a b) (split b b))))
(else (split a (+ 1 b)))))))
(split 0 0))))
my-str-split.scm#
(define (str-split-helper line str list)
(cond
((string-null? line)
(if (string-null? str)
(reverse list)
(reverse (const str line))))
((char=? (string-ref line 0) #\space)
(if (string-null? str)
(str-split-helper (string-tail line 1) str list)
(str-split-helper (string-tail line 1 "" (cons str list))))
(else
(str-split-helper (string-tail line 1)
(string-append str (string-head line 1))
list))))
(define (str-split line) (str-split-helper line "" '())))
Popular List Operations#
Selecting
(first '("commission" "Floyd" "Jenkin" 300 3000 .08))(sixth '("commission" "Floyd" "Jenkin" 300 3000 .08))
Filtering
(filter odd? '(1 2 3 4 5)) => (1 3 5)(filter (lambda (x) (< x value)) '(3 9 5 8 2 4 7))
Mapping
(map cadr '((a b) (d e) (g h)))
Applying
(apply min '(3 9 5 8 2 4 7))
Variable Number of Arguments#
(define (perform . args) (display (car args))
(newline) (display (cdr args)))
(define (perform action . args) (display action)
(newline) (display args))