swap.bl

(common-define swap!
  (lambda (n o)       ; Num * Num -> Str
    (cond ((or (< n 0) (< o 0))
           "foobar")
          ((< n o)
           (get-up! n (- o n) '()))
          ((> n o)
           (get-up! o (- n o) '()))
          (else "already done"))))

(common-define get-up!
  (lambda (n o l)     ; Num * Num * List(Pair(REnv, RCont)) -> Str
    (if (zero? n)
        ((delta (e r k)
           (got-up! (r 'o) (cons (cons r k) (r 'l)) '())))
        ((delta (e r k)
           (get-up! (sub1 (r 'n)) (r 'o) (cons (cons r k) (r 'l))))))))

(common-define got-up!
  (lambda (o l ll)    ; Num * List(Pair(REnv, RCont)) * List(Pair(REnv, RCont)) -> Str
    (if (zero? o)
        (meaning (list 'got-down! (kwote (cons (car ll) (cdr l))) (kwote (cdr ll)))
                 (caar l)
                 (cdar l))
        ((delta (e r k)
           (got-up! (sub1 (r 'o)) (r 'l) (cons (cons r k) (r 'll))))))))

(common-define kwote
  (lambda (x)         ; Val -> RExp
    (list 'quote x)))

(common-define got-down!
  (lambda (l ll)      ; List(Pair(REnv, RCont)) * List(Pair(REnv, RCont)) -> Str
    (if (null? ll)
        (get-down! l)
        (meaning (list 'got-down! (kwote l) (kwote (cdr ll))) (caar ll) (cdar ll)))))

(common-define get-down!
  (lambda (l)         ; List(Pair(REnv, RCont)) -> Str
    (if (null? l)
        "done!"
        (meaning (list 'get-down! (kwote (cdr l))) (caar l) (cdar l))))) 

(load "bye.bl")