HMM-Ising

(define (drop-right lst n)
  (reverse (drop (reverse lst) n)))

(define (hmm state N)
  (if (= N 0)
      '()
      (pair (observe state)
            (hmm (transition state) (- N 1)))))

(define (observe state)
  (map (lambda (x) (if (flip .9) x (not x)))
       state))

(define (language-transition state)
  (map (lambda (x) (if (flip .8) x (not x)))
       state))

(define (ising-factor a b)
  (flip (if (equal? a b) 1.0 0.5)))

(define (transition state)
  (first
   (mh-query
    1 10
    (define new-state (language-transition state))
    new-state
    (all (map ising-factor (drop new-state 1) (drop-right new-state 1))))))

(hmm '(#f #f #f) 4)