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46 lines
1.4 KiB
Racket
46 lines
1.4 KiB
Racket
#lang br
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(require "struct.rkt" "line.rkt" "misc.rkt")
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(provide b-end b-goto b-gosub b-return b-for b-next)
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(define (b-end) (raise (end-program-signal)))
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(define (b-goto num-expr)
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(raise (change-line-signal num-expr)))
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(define return-stack empty)
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(define (b-gosub num-expr)
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(let/cc return-cc
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(push! return-stack return-cc)
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(b-goto num-expr)))
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(define (b-return)
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(unless (pair? return-stack)
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(raise-line-error "return without gosub"))
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(define top-return-k (pop! return-stack))
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(top-return-k))
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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) <= >=) start x end))
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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))) |