ikarus/src/ikarus.lists.ss

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(library (ikarus lists)
(export $memq list? reverse last-pair memq memv member)
(import
(only (scheme) $car $cdr)
(except (ikarus) list? reverse last-pair memq memv member))
(define $memq
(lambda (x ls)
(let f ([x x] [ls ls])
(and (pair? ls)
(if (eq? x (car ls))
ls
(f x (cdr ls)))))))
(define list?
(letrec ([race
(lambda (h t)
(if (pair? h)
(let ([h ($cdr h)])
(if (pair? h)
(and (not (eq? h t))
(race ($cdr h) ($cdr t)))
(null? h)))
(null? h)))])
(lambda (x) (race x x))))
(define reverse
(letrec ([race
(lambda (h t ls ac)
(if (pair? h)
(let ([h ($cdr h)] [ac (cons ($car h) ac)])
(if (pair? h)
(if (not (eq? h t))
(race ($cdr h) ($cdr t) ls (cons ($car h) ac))
(error 'reverse "~s is a circular list" ls))
(if (null? h)
ac
(error 'reverse "~s is not a proper list" ls))))
(if (null? h)
ac
(error 'reverse "~s is not a proper list" ls))))])
(lambda (x)
(race x x x '()))))
(define last-pair
(letrec ([race
(lambda (h t ls last)
(if (pair? h)
(let ([h ($cdr h)] [last h])
(if (pair? h)
(if (not (eq? h t))
(race ($cdr h) ($cdr t) ls h)
(error 'last-pair "~s is a circular list" ls))
last))
last))])
(lambda (x)
(if (pair? x)
(let ([d (cdr x)])
(race d d x x))
(error 'last-pair "~s is not a pair" x)))))
(define memq
(letrec ([race
(lambda (h t ls x)
(if (pair? h)
(if (eq? ($car h) x)
h
(let ([h ($cdr h)])
(if (pair? h)
(if (eq? ($car h) x)
h
(if (not (eq? h t))
(race ($cdr h) ($cdr t) ls x)
(error 'memq "circular list ~s" ls)))
(if (null? h)
'#f
(error 'memq "~s is not a proper list" ls)))))
(if (null? h)
'#f
(error 'memq "~s is not a proper list" ls))))])
(lambda (x ls)
(race ls ls ls x))))
(define memv
(letrec ([race
(lambda (h t ls x)
(if (pair? h)
(if (eqv? ($car h) x)
h
(let ([h ($cdr h)])
(if (pair? h)
(if (eqv? ($car h) x)
h
(if (not (eq? h t))
(race ($cdr h) ($cdr t) ls x)
(error 'memv "circular list ~s" ls)))
(if (null? h)
'#f
(error 'memv "~s is not a proper list" ls)))))
(if (null? h)
'#f
(error 'memv "~s is not a proper list" ls))))])
(lambda (x ls)
(race ls ls ls x))))
(define member
(letrec ([race
(lambda (h t ls x)
(if (pair? h)
(if (equal? ($car h) x)
h
(let ([h ($cdr h)])
(if (pair? h)
(if (equal? ($car h) x)
h
(if (not (eq? h t))
(race ($cdr h) ($cdr t) ls x)
(error 'member "circular list ~s" ls)))
(if (null? h)
'#f
(error 'member "~s is not a proper list" ls)))))
(if (null? h)
'#f
(error 'member "~s is not a proper list" ls))))])
(lambda (x ls)
(race ls ls ls x))))
)