Add prolog module

test.scm

@@ -1,7 +1,8 @@
 (use-modules (d-)
-	     (d- json)
-	     (srfi srfi-1)
-	     (d- test))
+             (d- json)
+             (srfi srfi-1)
+             (d- test)
+             (d- prolog))
 
 (define-test-suite "~>"
   (define-test "unwrapped"
@@ -145,14 +146,57 @@
   (define-test "object"
     (assert-equal '() (json "{}"))
     (assert-equal '((cat . 1)
-		    (bat . #t)
-		    (rat . "yessir"))
-		  (json "{\"cat\": 1, \"bat\": true, \"rat\": \"yessir\"}"))
+                    (bat . #t)
+                    (rat . "yessir"))
+                  (json "{\"cat\": 1, \"bat\": true, \"rat\": \"yessir\"}"))
     (assert-equal '((butter . 1)
-		    (brownie))
-		  (json "{\"butter\": 1, \"brownie\": {}}"))
+                    (brownie))
+                  (json "{\"butter\": 1, \"brownie\": {}}"))
     (assert-equal '(1 2)
-		  (json "{\"hello\": 1, \"world\": 2}"
-			#:obj-acons
-			(lambda (_key value rest)
-			  (cons value rest))))))
+                  (json "{\"hello\": 1, \"world\": 2}"
+                        #:obj-acons
+                        (lambda (_key value rest)
+                          (cons value rest))))))
+
+(define-test-suite "prolog"
+  ;; Stolen verbatim from PAIP (Norvig 92)
+  (define-test "zebra"
+    (<- (member ?item (?item . ?rest)))
+    (<- (member ?item (?x . ?rest)) (member ?item ?rest))
+
+    (<- (nextto ?x ?y ?list) (iright ?x ?y ?list))
+    (<- (nextto ?x ?y ?list) (iright ?y ?x ?list))
+
+    (<- (iright ?left ?right (?left ?right . ?rest)))
+    (<- (iright ?left ?right (?x . ?rest))
+        (iright ?left ?right ?rest))
+
+    (<- (= ?x ?x))
+
+    (<- (zebra ?h ?w ?z)
+        (= ?h ((house norwegian ? ? ? ?)
+               ?
+               (house ? ? ? milk ?) ? ?))
+        (member (house englishman ? ? ? red) ?h)
+        (member (house spaniard dog ? ? ?) ?h)
+        (member (house ? ? ? coffee green) ?h)
+        (member (house ukrainian ? ? tea ?) ?h)
+        (iright (house ? ? ? ? ivory)
+                (house ? ? ? ? green) ?h)
+        (member (house ? snails winston ? ?) ?h)
+        (member (house ? ? kools ? yellow) ?h)
+        (nextto (house ? ? chesterfield ? ?)
+                (house ? fox ? ? ?) ?h)
+        (nextto (house ? ? kools ? ?)
+                (house ? horse ? ? ?) ?h)
+        (member (house ? ? luckystrike orange-juice ?) ?h)
+        (member (house japanese ? parliaments ? ?) ?h)
+        (nextto (house norwegian ? ? ? ?)
+                (house ? ? ? ? blue) ?h)
+
+        (member (house ?w ? ? water ?) ?h)
+        (member (house ?z zebra ? ? ?) ?h))
+    (define get-solution (?- (zebra ? ?water-drinker ?zebra-owner)))
+    (define solution (get-solution))
+    (assert-equal 'norwegian (assq-ref solution '?water-drinker))
+    (assert-equal 'japanese (assq-ref solution '?zebra-owner))))