mk: partitiono — split list by predicate

(partitiono pred l yes no) — yes is the elements of l where pred
succeeds; no is the rest. Conde dispatches on each element via the
predicate goal vs nafc-of-the-predicate, threading the head through
the matching output list.

Composes with intarith / membero / etc. for any predicate-shaped goal:
  (partitiono (fn (x) (lto-i x 5)) (list 1 7 2 8 3) yes no)
    yes -> (1 2 3); no -> (7 8)

5 new tests, 496/496 cumulative.

lib/minikanren/relations.sx

@@ -48,6 +48,14 @@
     (l1 l2 l3 result)
     (fresh (l12) (appendo l1 l2 l12) (appendo l12 l3 result))))
 
+(define
+  partitiono
+  (fn
+    (pred l yes no)
+    (conde
+      ((nullo l) (nullo yes) (nullo no))
+      ((fresh (a d y-rest n-rest) (conso a d l) (conde ((pred a) (conso a y-rest yes) (== no n-rest) (partitiono pred d y-rest n-rest)) ((nafc (pred a)) (== yes y-rest) (conso a n-rest no) (partitiono pred d y-rest n-rest))))))))
+
 (define
   membero
   (fn
@@ -80,6 +88,7 @@
       ((nullo l) (nullo r))
       ((fresh (a d res-rev) (conso a d l) (reverseo d res-rev) (appendo res-rev (list a) r))))))
 
+
 (define
   rev-acco
   (fn
@@ -88,7 +97,6 @@
       ((nullo l) (== result acc))
       ((fresh (a d acc-prime) (conso a d l) (conso a acc acc-prime) (rev-acco d acc-prime result))))))
 
-
 (define rev-2o (fn (l result) (rev-acco l (list) result)))
 
 (define palindromeo (fn (l) (fresh (rev) (reverseo l rev) (== l rev))))