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52 lines
1.5 KiB
Racket
52 lines
1.5 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-ccs empty)
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(define (b-gosub num-expr)
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(let/cc this-cc
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(push! return-ccs this-cc)
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(b-goto num-expr)))
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(define (b-return)
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(when (empty? return-ccs)
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(raise-line-error "return without gosub"))
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(define top-cc (pop! return-ccs))
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(top-cc (void)))
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(define next-funcs (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
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(let/cc loop-cc
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(hash-set! next-funcs
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'LOOP-ID
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(λ ()
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(define next-val
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(+ LOOP-ID STEP))
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(if (next-val
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. in-closed-interval? .
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START END)
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(loop-cc next-val)
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(hash-remove! next-funcs
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'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? next-funcs 'LOOP-ID)
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(raise-line-error
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(format "`next ~a` without for" 'LOOP-ID)))
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(define func (hash-ref next-funcs 'LOOP-ID))
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(func))) |