mk: numbero / stringo / symbolo type predicates

Ground-only type tests via project. Each succeeds iff its argument
walks to the corresponding host value type. Composes with membero for
type-filtered enumeration:

  (fresh (x) (membero x (list 1 "a" 2 "b" 3)) (numbero x) (== q x))
    -> (1 2 3)

12 new tests, 328/328 cumulative. Caveat: SX keywords are strings, so
(stringo :k) succeeds.

lib/minikanren/intarith.sx

@@ -54,3 +54,9 @@
     (project
       (a b)
       (if (and (number? a) (and (number? b) (not (= a b)))) succeed fail))))
+
+(define numbero (fn (x) (project (x) (if (number? x) succeed fail))))
+
+(define stringo (fn (x) (project (x) (if (string? x) succeed fail))))
+
+(define symbolo (fn (x) (project (x) (if (symbol? x) succeed fail))))

lib/minikanren/tests/types.sx

@@ -0,0 +1,52 @@
+;; lib/minikanren/tests/types.sx — type-predicate goals.
+
+(mk-test
+  "numbero-on-int"
+  (run* q (numbero 5))
+  (list (make-symbol "_.0")))
+(mk-test "numbero-on-string" (run* q (numbero "5")) (list))
+(mk-test "numbero-on-symbol" (run* q (numbero (quote x))) (list))
+(mk-test "numbero-on-list" (run* q (numbero (list 1))) (list))
+
+(mk-test
+  "stringo-on-string"
+  (run* q (stringo "hi"))
+  (list (make-symbol "_.0")))
+(mk-test "stringo-on-int" (run* q (stringo 5)) (list))
+(mk-test
+  "stringo-on-keyword"
+  (run* q (stringo :k))
+  (list (make-symbol "_.0")))  ;; SX keywords ARE strings
+
+(mk-test
+  "symbolo-on-symbol"
+  (run* q (symbolo (quote x)))
+  (list (make-symbol "_.0")))
+(mk-test "symbolo-on-string" (run* q (symbolo "x")) (list))
+(mk-test "symbolo-on-int" (run* q (symbolo 5)) (list))
+
+;; --- combine with membero for type-filtered enumeration ---
+
+(mk-test
+  "membero-numbero-filter"
+  (run*
+    q
+    (fresh
+      (x)
+      (membero x (list 1 "a" 2 "b" 3))
+      (numbero x)
+      (== q x)))
+  (list 1 2 3))
+
+(mk-test
+  "membero-stringo-filter"
+  (run*
+    q
+    (fresh
+      (x)
+      (membero x (list 1 "a" 2 "b" 3))
+      (stringo x)
+      (== q x)))
+  (list "a" "b"))
+
+(mk-tests-run!)

plans/minikanren-on-sx.md

@@ -173,6 +173,11 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-08** — **numbero / stringo / symbolo (type predicates)**: ground-only
+  type tests via project. Compose with `membero` for type-filtered enumeration:
+  `(fresh (x) (membero x (1 "a" 2 "b" 3)) (numbero x) (== q x))` → `(1 2 3)`.
+  Note: SX keywords are strings, so `(stringo :k)` succeeds. 12 new tests,
+  328/328 cumulative.
 - **2026-05-08** — **Graph reachability via patho**: classic miniKanren
   graph search. `edgeo` looks up edges in a fact list via `membero`; `patho`
   recursively builds paths via direct-edge OR (one edge + recurse + cons).