Finite Mixture Model

(define (zip xs1 xs2) 
  (if (or (is_null xs1) (is_null xs2)) '() 
      (pair 
       (pair (first xs1) (pair (first xs2) '()))
       (zip (rest xs1) (rest xs2)))))

(define (soft-eq x y) 
  (factor (if (equal? x y) 0.0 (log 0.1))))

(define samples
  (mh-query 10 100
   (define objects '(bob jane mary steve))
   (define object-indices (iota (length objects)))
   (define observed-features '(#t #t #f #f))
   (define categories '(a b c))
   (define cat-indices (iota (length categories)))
   (define pseudo-counts (repeat (length categories) (lambda () 1.0)))
   (define cats-dist (dirichlet pseudo-counts))
   (define cat-weights 
     (map (lambda (cat) (beta 1.0 1.0)) 
          categories))
   (define types 
     (map (lambda (obj) (multinomial cat-indices cats-dist)) 
          objects))
   (define observations 
     (map (lambda (obj-index) 
            (flip (list-ref cat-weights (list-ref types obj-index)))) 
          object-indices))
   (define res 
     (map (lambda (cat-index) (list-ref categories cat-index)) 
          types))
   (define constr 
     (map (lambda (obs12) 
            (soft-eq (first obs12) (second obs12))) 
          (zip observations observed-features)))
   (define sample (pair res constr)) 
   sample 
   #t))

samples