A doubly-intractable HMM, meant as a toy model for speech recognition with articulatory contraints.

```
(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 (factor a b)
(flip (if (equal? a b) 1.0 0.5)))
(define (transition state)
(mh-query
10 10
(define new-state (language-transition state))
new-state
(all (map factor (drop new-state 1) (drop-right new-state 1)))))
(hmm '(#f #f #f) 4)
```