34 lines
944 B
Racket
34 lines
944 B
Racket
#lang racket
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(define instruction
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'(("B" "s1") . ("X" "R" "s2")))
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;;; The tape utility functions should hide the actual tape
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;;; representation.
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(define (tape-lookup tape position)
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(unless (hash-has-key? tape position)
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(hash-set! tape position "B"))
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(hash-ref tape position))
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(define (tape-write tape position sym)
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(hash-set! tape position sym))
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(define (head-update head head_dir)
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(cond
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[(equal? head_dir "R") (+ head 1)]
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[(equal? head_dir "L") (- head 1)]
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[else (error "invalid head direction")]))
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(define (turing-update tape head state instruction)
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(tape-write tape head (car instruction))
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(values tape
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(head-update head (car (cdr instruction)))
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(car (cdr (cdr instruction)))))
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(define (turing-instruction tape instructions)
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(for (instruction instructions)
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;; does the car match the tape and the head position?
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;; if it does, break the loop and return the instruction
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;; keep going
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))
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