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(export
append
caar
cadr
car
cdar
cddr
cdr
cons
length
list
list-copy
list-ref
list-set!
list-tail
list?
make-list
null?
pair?
reverse
set-car!
set-cdr!)
(import (only (csc builtins)
call-builtin))
(begin
(define-record-type <pair>
(cons x y)
pair?
(x car set-car!)
(y cdr set-cdr!))
(define (caar pair)
(car (car pair)))
(define (cadr pair)
(car (cdr pair)))
(define (cdar pair)
(cdr (car pair)))
(define (cddr pair)
(cdr (cdr pair)))
(define (null? obj)
(call-builtin eq? obj '()))
(define (list? obj)
(cond
((null? obj) #t)
((not (pair? obj)) #f)
(else
(let loop ((tortoise obj)
(hare (cdr obj)))
(cond
((null? hare) #t)
((not (pair? hare)) #f)
((null? (cdr hare)) #t)
((not (pair? (cdr hare))) #f)
((eq? tortoise hare) #f) ; cycle detected
(else
(loop (cdr tortoise)
(cddr hare))))))))
(define make-list
(case-lambda
((k)
(make-list k #f))
((k fill)
(let loop ((k k)
(acc '()))
(if (zero? k)
acc
(loop (- k 1) (cons fill acc)))))))
(define (list . args)
args)
(define (length l)
(let loop ((l l)
(n 0))
(if (null? l)
n
(loop (cdr l) (+ 1 n)))))
(define (append2 l1 l2)
(let loop ((l1 l1))
(if (null? l1)
l2
(cons (car l1) (loop (cdr l1))))))
(define (append . ls)
(let loop ((ls ls))
(cond
((null? ls) '())
((null? (cdr ls))
(car ls))
(else
(append2 (car ls)
(loop (cdr ls)))))))
(define (reverse l)
(let loop ((l l)
(acc '()))
(if (null? l)
acc
(loop (cdr l) (cons (car l) acc)))))
(define (list-tail l k)
(if (zero? k)
l
(list-tail (cdr l) (- k 1))))
(define (list-ref l k)
(car (list-tail l k)))
(define (list-set! l k obj)
(let loop ((l l)
(k k))
(if (zero? k)
(set-car! l obj)
(loop (cdr l) (- k 1)))))
(define (list-copy obj)
(if (pair? l)
(cons (car l) (list-copy (cdr l)))
l)))
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