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POdrscheme - finite state machine
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copied!<p>thanks to people at this great site I managed to put together code that is nearly complete and working. I have one final question.</p> <p>here is the code:</p> <pre><code> (define (chartest ch) (lambda (x) (char=? x ch))) (define fsm-trans '((A (lambda (x) (string=? x "a") B), (B (lambda (x) (string=? x "a") C))))) (define (find-next-state state ch trl) (cond [(empty? trl) false] [(and (symbol=? state (first (first trl))) ((second (first trl)) ch)) (third (first trl))] [else (find-next-state state ch (rest trl))])) (define fsm-final '(C)) (define start-state 'A) (define (run-fsm start trl final input) (cond [(empty? input) (cond [(member start final) true] [else false])] [else (local ((define next (find-next-state start (first input) trl))) (cond [(boolean? next) false] [else (run-fsm next trl final (rest input))]))])) (run-fsm start-state fsm-trans fsm-final (string->list "ac")) </code></pre> <p>i have a problem with the transition function find-next-state. How can I define it in order to test the incoming characters and based on this either return true value when the fsm reaches final state or false value when it doesn't?</p> <p>Thank you for your answer.</p> <p>UPDATE:</p> <p>Thank you for your answer and I am sorry that the code is confusing. I have repaired the definition of transtitions which now looks like this:</p> <pre><code> (define fsm-trans '((A (lambda (x) (string=? x "a") B) (B (lambda (x) (string=? x "a") C))))) </code></pre> <p>But now I am trying to define the transition function. When I haven't had fixed transition character and I used char-alphabetic? and char-numeric?, these lines of code worked like a charm:</p> <pre><code> (define (find-next-state state ch trl) (cond [(empty? trl) false] [(and (symbol=? state (first (first trl))) ((second (first trl)) ch)) (third (first trl))] [else (find-next-state state ch (rest trl))])) </code></pre> <p>But what should I change to work with the new definition of states in fsm-trans? When this code is entered in DrScheme, it shows up an error with line: ((second (first trl)) ch)).</p> <p>Thank you for your further assistance!</p>

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