diff --git a/beautiful-racket/br/demo/basic/expander.rkt b/beautiful-racket/br/demo/basic/expander.rkt index a89de60..e8bac18 100644 --- a/beautiful-racket/br/demo/basic/expander.rkt +++ b/beautiful-racket/br/demo/basic/expander.rkt @@ -18,7 +18,7 @@ (gather-unique-ids #'(PROGRAM-LINE ...)))]) #'(#%module-begin (define UNIQUE-ID 0) ... - (run PROGRAM-LINE ...)))) + (run PROGRAM-LINE ... (line #f (statement "end")))))) ; #%app and #%datum have to be present to make #%top work (define-macro (basic-top . ID) @@ -53,13 +53,11 @@ (with-handlers ([end-program-signal? void]) (for/fold ([program-counter 0]) ([i (in-naturals)]) - (if (= program-counter (vector-length lines)) - (basic:end) - (let* ([line-thunk ($line-thunk (vector-ref lines program-counter))] - [maybe-line-number (line-thunk)]) - (if (number? maybe-line-number) - (find-index maybe-line-number) - (add1 program-counter)))))))) + (let* ([line-thunk ($line-thunk (vector-ref lines program-counter))] + [maybe-line-number (line-thunk)]) + (if (number? maybe-line-number) + (find-index maybe-line-number) + (add1 program-counter))))))) (define return-stack empty) @@ -70,8 +68,8 @@ (struct $line (number thunk) #:transparent) (define-macro (line NUMBER . STATEMENTS) - #'($line NUMBER (λ () (with-handlers ([end-line-signal? (λ _ #f)]) - . STATEMENTS)))) + #'($line NUMBER (λ () (with-handlers ([end-line-signal? (λ _ #f)]) + . STATEMENTS)))) (define-macro statement [(statement ID "=" EXPR) #'(set! ID EXPR)] @@ -170,31 +168,27 @@ #'(basic:for VAR START-VALUE END-VALUE 1)] [(_ VAR START-VALUE END-VALUE STEP-VALUE) #'(begin - (cond - [(and (pair? for-stack) - (eq? 'VAR (car (car for-stack)))) - ;; we're already in the midst of a loop, so abort the rest of the line - (raise-end-line-signal)] - [else - ;; 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 - (push-for-stack (cons 'VAR - (λ () ; thunk that increments counter & teleports back to beginning of loop - (define next-val (+ VAR STEP-VALUE)) - (when (<= next-val END-VALUE) - (set! VAR next-val) - (return-point-for-next)))))) - (raise-end-line-signal)]))]) - -(define (handle-next [stack-selector-proc car]) - (unless (pair? for-stack) - (error 'next "for-stack is empty")) - (let ([for-thunk (cdr (stack-selector-proc for-stack))]) - (unless (for-thunk) - (pop-for-stack)))) - -(define-macro basic:next - [(_ VAR) #'(handle-next (λ(stack) (assq 'VAR stack)))] ; named `next` means find var in stack - [(_) #'(handle-next)]) ; plain `next` implies var on top of stack + ;; 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 + (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)))) + #f))]) ; return value for first visit to line + +(define (handle-next [which #f]) + (unless (pair? for-stack) (error 'next "for-stack is empty")) + (define for-thunk (cdr (if which + (assq which for-stack) + (car for-stack)))) + (for-thunk)) + +(define-macro (basic:next VAR ...) + #'(handle-next 'VAR ...)) \ No newline at end of file diff --git a/beautiful-racket/br/demo/basic/for.bas b/beautiful-racket/br/demo/basic/for.bas index 473fbc3..4b00c5e 100644 --- a/beautiful-racket/br/demo/basic/for.bas +++ b/beautiful-racket/br/demo/basic/for.bas @@ -1,5 +1,8 @@ #lang br/demo/basic -10 for A=1 to 5 step 3 +10 for A=1 to 3 20 print A -30 next +21 for B=5 to 8 +22 print B +23 next B +30 next A 40 print "yay" \ No newline at end of file