Inside/Outside algorithm specialized to simple example

gistfile1.scm

(import (printing)
        (_srfi :1))

(define start-params
  '(1/3 1/3 1/3))

(define (likelihood params)
  (* (list-ref params 0) 
     (list-ref params 0)
     (list-ref params 1)
     (list-ref params 2)))

(define (exp-counts idx params)
  ;; Rationale:
  ;; There are always 2 occurrences of S -> r S, 1 of S -> g S, and 1 of S -> b.
  (cond [(equal? 0 idx)
         (*
           (/ 1 (likelihood params))
             (* 2 (likelihood params)))]
        [(equal? 1 idx)
         (*
           (/ 1 (likelihood params))
             (* 1 (likelihood params)))]
        [(equal? 2 idx)
         (*
           (/ 1 (likelihood params))
             (* 1 (likelihood params)))]))

(define (normalize params)
  (let* ([factor (apply + params)])
    (map (lambda (p) (/ p factor)) params)))

(define (io-iteration params)
  (let* ([exp-counts (map (lambda (i) (exp-counts i params)) (iota (length params)))]
         )
    (normalize exp-counts)))


(define (io-n-iter n start)
  (cond [(= 0 n) start]
        [else
          (begin 
            (print "current params ~s" start)
            (io-n-iter (- n 1) (io-iteration start)))]))


(print (io-n-iter 10 start-params))

;; output:
;; current params (1/3 1/3 1/3)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; current params (1/2 1/4 1/4)
;; (1/2 1/4 1/4)