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This commit is contained in:
Matthew Butterick 2016-06-03 22:29:19 -07:00
parent 83a1090754
commit 6ad59477cd
2 changed files with 11 additions and 14 deletions
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2
beautiful-racket/br/demo/basic/aceyducey.bas
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@ -11,7 +11,7 @@
80 PRINT"IF YOU DO NOT WANT TO BET, INPUT A 0"
100 N=100
110 Q=100
120 PRINT "YOU NOW HAVE";Q;"DOLLARS."
120 PRINT "YOU NOW HAVE ";Q;" DOLLARS."
130 PRINT
140 GOTO 260
210 Q=Q+M

23
beautiful-racket/br/demo/basic/expander.rkt
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@ -66,7 +66,7 @@
(set! return-stack (cons return-k return-stack))
(basic:goto where)))
(struct $line (number thunk) #:transparent)
(struct $line (number thunk))
(define-macro (line NUMBER . STATEMENTS)
#'($line NUMBER (λ () (with-handlers ([end-line-signal? (λ _ #f)])
. STATEMENTS))))
@ -168,19 +168,16 @@
#'(basic:for VAR START-VALUE END-VALUE 1)]
[(_ VAR START-VALUE END-VALUE STEP-VALUE)
#'(begin
;; initialize the loop counter
(statement VAR "=" START-VALUE)
;; create a point for the `next` statement to return to, using a continuation
(let/cc return-point-for-next
(statement VAR "=" START-VALUE) ; initialize the loop counter
(let/cc return-k ; create a return point
(push-for-stack (cons 'VAR
(procedure-rename
(λ () ; thunk that increments counter & teleports back to beginning of loop
(define next-val (+ VAR STEP-VALUE))
(if (<= next-val END-VALUE)
(begin
(set! VAR next-val)
(return-point-for-next #f)) ; return value for subsequent visits to line
(pop-for-stack))) (format-datum "~a-incrementer" 'VAR))))
(λ () ; thunk that increments counter & teleports back to beginning of loop
(define next-val (+ VAR STEP-VALUE))
(if (<= next-val END-VALUE)
(begin
(set! VAR next-val)
(return-k #f)) ; return value for subsequent visits to line
(pop-for-stack)))))
#f))]) ; return value for first visit to line
(define (handle-next [which #f])