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@Pet3ris
Created Dec 17, 2012
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; Temporal logic programming with explicit time using core.logic
; we assume relations s, <o and constants zero, one, four are defined as in
; https://github.com/frenchy64/Logic-Starter/blob/master/src/logic_introduction/numbers.clj
; we start by using 'next' to define a Fibonacci relation
; that is equal to F(n) at time n
; We use the small trick that if a number
; has a predecessor and then another, then it is at least 2
(defn fib [v t]
(conde
((== t zero) (== v 0))
((== t one) (== v 1))
((fresh [p pp x y]
(s p t)
(s pp p)
(fib x p)
(fib y pp)
(project [x y]
(== v (+ x y)))))))
(run* [q] (fib q four))
;=> (3)
(run 10 [q] (fresh [v t] (fib v t) (== q [t v])))
;=> ([0 0] [(0) 1] [((0)) 1] [(((0))) 2] [((((0)))) 3]
; [(((((0))))) 5] [((((((0)))))) 8] [(((((((0))))))) 13]
; [((((((((0)))))))) 21] [(((((((((0))))))))) 34])
; Is a fibonacci number eventually bigger than 10?
(run 1 [q]
(fresh [v t]
(fib v t)
(project [v]
(if (> v 10) succeed fail))))
;=> (_.0)
; Always true past t = 4
(defn pastfour [t]
(<o four t))
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