1D Ising

(define (all-but-last xs)
  (cond ((null? xs) (error "all-but-last got empty list!"))
        ((null? (rest xs)) '())
        (else (pair (first xs) (all-but-last (rest xs))))))

(define (all xs)
  (if (null? xs)
      #t
      (and (first xs)
           (all (rest xs)))))

(define (noisy-equal? a b)
  (flip (if (equal? a b) 1.0 0.2)))

(define samples
  (mh-query 10 5
            (define bits (repeat 10 (lambda () (if (flip) 1 0))))
            bits
            (all (map noisy-equal? (rest bits) (all-but-last bits)))))

(for-each display samples)    

(define ising-length 20)
(define non-match-cost (log 0.1))

;; abuses map
(define (bigram xs) 
  (map list xs (cdr xs)))

(define samples
  (mh-query 
    50 50
    (define (eql x y) (factor (if (= x y) 0.0 non-match-cost)))
    (define xs (repeat ising-length (lambda () (if (flip) 0 1))))
    (for-each (lambda (xy) (eql (car xy) (car (cdr xy)))) (bigram xs))
    xs
    #t))

(car (reverse samples))