#lang pl

(define-type Token = (U Symbol Integer))

(: in? : Symbol (Listof Symbol) -> Boolean)
(define (in? s l) (and (not (null? l)) (not (and (not (symbol=? s (first l))) (not (in? s (rest l)))))))

(test (in? 'a '(b d e a f e)))
(test (in? 'a '(b x e a x e)))
(test (in? 'a '(a b d e a f e)))
(test (in? 'a '(b d e a f e a)))
(test (not (in? 'a '(b d e f e))))
(test (not (in? 'a '())))

#|
(: abc : String -> Boolean)
; Identifies strings that match "(ab(c+))+"
(define abc (automaton one (four)
                       [one : (a -> two)]
                       [two : (b -> three)]
                       [three : (c -> four)]
                       [four : (c -> four) (a -> two)]))

(test (abc "abccc"))
(test (abc "abcccabc"))
(test (not (abc "ab")))
(test (not (abc "q")))
(test (not (abc "abcb")))
(test (not (abc "abcab")))
|#