mk: zip-with-o — element-wise combine of two lists

Like Haskell's zipWith but relational. (zip-with-o rel l1 l2 result)
applies a 3-arg combiner relation pointwise: rel l1[i] l2[i] result[i].

  (zip-with-o pluso-i (list 1 2 3) (list 10 20 30) q)
    -> ((11 22 33))

  (zip-with-o (fn (a b r) (== r (list a b))) (list :x :y) (list 1 2) q)
    -> (((:x 1) (:y 2)))

Different-length lists fail.

5 new tests, 551/551 cumulative.

lib/minikanren/tests/zip-with-o.sx

@@ -0,0 +1,52 @@
+;; lib/minikanren/tests/zip-with-o.sx — element-wise combine of two lists.
+
+(mk-test
+  "zip-with-o-empty"
+  (run* q (zip-with-o pluso-i (list) (list) q))
+  (list (list)))
+
+(mk-test
+  "zip-with-o-pluso-i"
+  (run*
+    q
+    (zip-with-o
+      pluso-i
+      (list 1 2 3)
+      (list 10 20 30)
+      q))
+  (list (list 11 22 33)))
+
+(mk-test
+  "zip-with-o-times-i"
+  (run*
+    q
+    (zip-with-o
+      *o-i
+      (list 2 3 4)
+      (list 5 6 7)
+      q))
+  (list (list 10 18 28)))
+
+(mk-test
+  "zip-with-o-different-length-fails"
+  (run*
+    q
+    (zip-with-o
+      pluso-i
+      (list 1 2)
+      (list 1 2 3)
+      q))
+  (list))
+
+(mk-test
+  "zip-with-o-non-arith-rel"
+  (run*
+    q
+    (zip-with-o
+      (fn (a b r) (== r (list a b)))
+      (list :x :y)
+      (list 1 2)
+      q))
+  (list (list (list :x 1) (list :y 2))))
+
+(mk-tests-run!)