Stochastic Logic Programs (SLP) style probabilistic logic programming in miniKanren
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Stochastic Logic Programs (SLP) style probabilistic logic programming in miniKanren, based on Stephen Muggleton's paper, 'Stochastic Logic Programs':

Code by Rebecca Swords and William E. Byrd, based on core miniKanren.

slpKanren extends core miniKanren with one relational operator (condp) and two interface operators (run-prob and run-prob*):

(condp [prob-exp g g* ...] ...)

condp is identitical to conde, except that the first expression in each clause must evaluate to a real number representing the probability associated with that clause. Operationally, condp behaves identically to conde, other than associating a probability with each successful clause. In other words, condp and conde produce the same answers, in the same order; however, condp associates a probility with each answer.

(run-prob n (x) g0 g ...)
(run-prob* (x) g0 g ...)

run-prob and run-prob* are identical to run and run*, except that the probability associated with each answer is also returned.

This implementation also includes two debugging goals, which can be used to examine the substition: print-substo and print-prob-substo.

Example slpKanren program, adapted from the Muggleton paper:

;;; stochastic automaton
(define sa
  (lambda (S)
    (letrec ([q0 (lambda (S)
                   (exist (S^)
                        (== `(a . ,S^) S)
                        (q0 S^)]
                        (== `(b . ,S^) S)
                        (q1 S^)])))]
             [q1 (lambda (S)
                   (exist (S^)
                        (== `(b . ,S^) S)
                        (q1 S^)]
                        (== `(c . ,S^) S)
                        (q2 S^)])))]
             [q2 (lambda (S) (== '() S))])
      (q0 S))))

and associated test cases:

(test "sa-1"
  (run-prob 10 (q) (sa q))
  '(((b c) . 0.18)
    ((b b c) . 0.126)
    ((a b c) . 0.072)
    ((b b b c) . 0.08819999999999999)
    ((b b b b c) . 0.06173999999999999)
    ((a b b c) . 0.0504)
    ((b b b b b c) . 0.043217999999999986)
    ((b b b b b b c) . 0.03025259999999999)
    ((a a b c) . 0.0288)
    ((a b b b c) . 0.03528)))
(test "sa-2"
  (run-prob 1 (q) (== '(a b b c) q) (sa q))
  `(((a b b c) . ,(* 0.4 0.6 0.7 0.3))))

All Scheme code tested under Petite Chez Scheme Version 8.4.