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30 lines
1018 B
Racket
30 lines
1018 B
Racket
8 years ago
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#lang br
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(require "misc.rkt" "line.rkt")
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(provide b-for b-next)
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(define thunk-table (make-hasheq))
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(define-macro-cases b-for
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[(_ LOOP-ID START END) #'(b-for LOOP-ID START END 1)]
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[(_ LOOP-ID START END STEP)
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#'(b-let LOOP-ID (let/cc loop-cc
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(hash-set! thunk-table
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'LOOP-ID
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(λ ()
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(define next-val (+ LOOP-ID STEP))
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(if (next-val . in-closed-interval? . START END)
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(loop-cc next-val)
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(hash-remove! thunk-table 'LOOP-ID))))
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START))])
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(define (in-closed-interval? x start end)
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(if (< start end)
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(<= start x end)
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(<= end x start)))
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(define-macro (b-next LOOP-ID)
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#'(begin
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(unless (hash-has-key? thunk-table 'LOOP-ID)
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(raise-line-error "next without for"))
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(define thunk (hash-ref thunk-table 'LOOP-ID))
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(thunk)))
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