replo.clj

(ns replo                                                                                                                                                                  
  (:refer-clojure :exclude [==])                                                                                                                                             
  (:use [clojure.core.logic]))                                                                                                                                                    
                                                                                                                                                                                  
(defn replo 
  "A relation between two sequences in and out, such that out is the                                                                                                              
same as in, except that all occurences of k have been replaced with                                                                                                               
v."
  [k v in out]                                                                                                                                                          
  (matche [in out]                                                                                                                                                                
   [[() ()]]                                                                                                                                                                      
   [[(k . d) (v . e)] (replo k v d e)]                                                                                                                                            
   [[(a . d) (b . e)]                                                                                                                                                             
    (conda                                                                                                                                                                        
     [(replo k v a b) (replo k v d e)]                                                                                                                                            
     [(== a b) (replo k v d e)])]))                                                                                                                                               
                                                                                                                                                                                  
(run 1 [q]                                                                                                                                                                        
  (fresh [k v in out]                                                                                                                                                          
    (== k 'p)                                                                                                                                                             
    (== v 'q)                                                                                                                                                             
    (== in '((p) x))                                                                                                                                                      
  ;;(== out '((q) x))                                                                                                                                                   
    (replo k v in out)                                                                                                                                                    
    (== q [k v in out])))