[else (tz1 (pair (cons (nextchar z) (saved z)) (rest z)))]))
; using explicit continuations
-(define (tc1 l k)
+(define (tc0 l k)
(cond
[(null? l) (reverse (k '()))]
+ [(eqv? #\S (car l)) (tc0 (cdr l) (compose k k))]
+ [else (tc0 (cdr l) (lambda (tail) (cons (car l) (k tail))))]))
+
+; improvement: if we flip the order of cons and k in the last line, we can avoid the need to reverse
+(define (tc1 l k)
+ (cond
+ [(null? l) (k '())]
[(eqv? #\S (car l)) (tc1 (cdr l) (compose k k))]
- [else (tc1 (cdr l) (lambda (tail) (cons (car l) (k tail))))]))
+ [else (tc1 (cdr l) (lambda (tail) (k (cons (car l) tail))))]))
; using implicit continuations (reset/shift)
(define (tr1 l)
(shift k
(cond
- [(null? l) (reverse (k '()))]
+ [(null? l) (k '())]
[(eqv? #\S (car l)) ((compose k k) (tr1 (cdr l)))]
- [else ((lambda (tail) (cons (car l) (k tail))) (tr1 (cdr l)))])))
+ [else ((lambda (tail) (k (cons (car l) tail))) (tr1 (cdr l)))])))
; wrapper functions, there's a (test) function at the end
[else (tz3 (pair (cons (nextchar z) (saved z)) (rest z)))]))
; using explicit continuations
-; there are several working solutions
-; but it's a bit tricky to get the reverses in the right place, and the order of appending right
(define (tc3 l k)
(cond
- [(null? l) (reverse (k '()))]
- [(eqv? #\# (car l)) (append (reverse (k '())) (tc3 (cdr l) identity))]
+ [(null? l) (k '())]
+ ; [(eqv? #\# (car l)) (append (k '()) (tc3 (cdr l) identity))]
+ [(eqv? #\# (car l)) (k (tc3 (cdr l) identity))]
[(eqv? #\S (car l)) (tc3 (cdr l) (compose k k))]
- [else (tc3 (cdr l) (lambda (tail) (cons (car l) (k tail))))]))
+ [else (tc3 (cdr l) (lambda (tail) (k (cons (car l) tail))))]))
; using implicit continuations (reset/shift)
(define (tr3 l)
(shift k
(cond
- [(null? l) (reverse (k '()))]
- [(eqv? #\# (car l)) (append (reverse (k '())) (reset (tr3 (cdr l))))]
+ [(null? l) (identity (k '()))]
+ ; [(eqv? #\# (car l)) (append (k '()) (reset (tr3 (cdr l))))]
+ [(eqv? #\# (car l)) (k (reset (tr3 (cdr l))))]
[(eqv? #\S (car l)) ((compose k k) (tr3 (cdr l)))]
- [else ((lambda (tail) (cons (car l) (k tail))) (tr3 (cdr l)))])))
+ [else ((lambda (tail) (k (cons (car l) tail))) (tr3 (cdr l)))])))
(define (tz4 s)
(list->string (tz3 (cons '() (string->list s)))))
(equal? (t1 inp) (t2 inp)))
(and
(equal? (tz2 "abSd") "ababd")
+ (cmp (lambda (s) (list->string (tc0 (string->list s) identity))) tz2 "abSd")
(cmp tc2 tz2 "abSd")
(cmp tr2 tz2 "abSd")
(equal? (tz2 "aSbS") "aabaab")
+ (cmp (lambda (s) (list->string (tc0 (string->list s) identity))) tz2 "aSbS")
(cmp tc2 tz2 "aSbS")
(cmp tr2 tz2 "aSbS")
(equal? (tz4 "ab#ceSfSd") "abcecefcecefd")