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@ -18,7 +18,7 @@
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(gather-unique-ids #'(PROGRAM-LINE ...)))])
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#'(#%module-begin
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(define UNIQUE-ID 0) ...
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(run PROGRAM-LINE ...))))
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(run PROGRAM-LINE ... (line #f (statement "end"))))))
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; #%app and #%datum have to be present to make #%top work
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(define-macro (basic-top . ID)
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@ -53,13 +53,11 @@
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(with-handlers ([end-program-signal? void])
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(for/fold ([program-counter 0])
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([i (in-naturals)])
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(if (= program-counter (vector-length lines))
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(basic:end)
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(let* ([line-thunk ($line-thunk (vector-ref lines program-counter))]
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[maybe-line-number (line-thunk)])
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(if (number? maybe-line-number)
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(find-index maybe-line-number)
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(add1 program-counter))))))))
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(add1 program-counter)))))))
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(define return-stack empty)
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@ -170,31 +168,27 @@
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#'(basic:for VAR START-VALUE END-VALUE 1)]
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[(_ VAR START-VALUE END-VALUE STEP-VALUE)
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#'(begin
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(cond
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[(and (pair? for-stack)
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(eq? 'VAR (car (car for-stack))))
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;; we're already in the midst of a loop, so abort the rest of the line
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(raise-end-line-signal)]
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[else
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;; initialize the loop counter
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(statement VAR "=" START-VALUE)
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;; create a point for the `next` statement to return to, using a continuation
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(let/cc return-point-for-next
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(push-for-stack (cons 'VAR
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(procedure-rename
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(λ () ; thunk that increments counter & teleports back to beginning of loop
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(define next-val (+ VAR STEP-VALUE))
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(when (<= next-val END-VALUE)
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(if (<= next-val END-VALUE)
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(begin
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(set! VAR next-val)
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(return-point-for-next))))))
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(raise-end-line-signal)]))])
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(define (handle-next [stack-selector-proc car])
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(unless (pair? for-stack)
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(error 'next "for-stack is empty"))
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(let ([for-thunk (cdr (stack-selector-proc for-stack))])
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(unless (for-thunk)
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(pop-for-stack))))
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(define-macro basic:next
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[(_ VAR) #'(handle-next (λ(stack) (assq 'VAR stack)))] ; named `next` means find var in stack
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[(_) #'(handle-next)]) ; plain `next` implies var on top of stack
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(return-point-for-next #f)) ; return value for subsequent visits to line
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(pop-for-stack))) (format-datum "~a-incrementer" 'VAR))))
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#f))]) ; return value for first visit to line
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(define (handle-next [which #f])
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(unless (pair? for-stack) (error 'next "for-stack is empty"))
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(define for-thunk (cdr (if which
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(assq which for-stack)
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(car for-stack))))
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(for-thunk))
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(define-macro (basic:next VAR ...)
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#'(handle-next 'VAR ...))
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