mk: matche keyword pattern fix + classic puzzles

matche-pattern->expr now treats keyword patterns as literals that emit
themselves bare, rather than wrapping in (quote ...). SX keywords
self-evaluate to their string name; quoting them flips them to a
keyword type that does not unify with the bare-keyword usage at the
target site. This was visible only as a test failure on the diffo
clauses below — tightened the pattern rules.

tests/classics.sx exercises three end-to-end miniKanren programs:
  - 3-friend / 3-pet permutation puzzle
  - grandparent inference over a fact list (membero + fresh)
  - symbolic differentiation dispatched by matche on
    :x / (:+ a b) / (:* a b)

228/228 cumulative.

lib/minikanren/matche.sx

@@ -5,33 +5,30 @@
 ;;     (PATTERN2 g1 ...)
 ;;     ...)
 ;;
-;; Each clause unifies TARGET with PATTERN, introducing a fresh variable
-;; for every plain symbol in the pattern, and runs its goal body. The
-;; pattern grammar:
-;;
+;; Pattern grammar:
 ;;   _                 wildcard — fresh anonymous var
 ;;   x                 plain symbol — fresh var, bind by name
-;;   ATOM              literal (number, string, keyword, boolean) — must equal
+;;   ATOM              literal (number, string, boolean) — must equal
+;;   :keyword          keyword literal — emitted bare (keywords self-evaluate
+;;                     to their string name in SX, so quoting them changes
+;;                     their type from string to keyword)
 ;;   ()                empty list — must equal
 ;;   (p1 p2 ... pn)    list pattern — recurse on each element
 ;;
 ;; The macro expands to a `conde` whose clauses are
-;;   `((fresh (vars...) (== target pat-expr) body...))`.
+;;   `((fresh (vars-in-pat) (== target pat-expr) body...))`.
 ;;
-;; Fixed-length list patterns only — no rest patterns. To match "head + rest",
-;; use `(fresh (a d) (conso a d target) body)` directly.
+;; Repeated symbol names within a pattern produce the same fresh var, so
+;; they unify by `==`. Fixed-length list patterns only — head/tail
+;; destructuring uses `(fresh (a d) (conso a d target) body)` directly.
 ;;
 ;; Note: the macro builds the expansion via `cons` / `list` rather than a
-;; quasiquote — the quasiquote expander does not recurse into lambda
-;; bodies, which broke the natural `\`(matche-clause (quote ,target) cl)`
-;; spelling.
+;; quasiquote — quasiquote does not recurse into nested lambda bodies in
+;; SX, so `\`(matche-clause (quote ,target) cl)` left literal
+;; `(unquote target)` in the output.
 
 (define matche-symbol-var? (fn (s) (symbol? s)))
 
-(define
-  matche-collect-vars
-  (fn (pat) (matche-collect-vars-acc pat (list))))
-
 (define
   matche-collect-vars-acc
   (fn
@@ -43,6 +40,10 @@
         (reduce (fn (a p) (matche-collect-vars-acc p a)) acc pat))
       (:else acc))))
 
+(define
+  matche-collect-vars
+  (fn (pat) (matche-collect-vars-acc pat (list))))
+
 (define
   matche-pattern->expr
   (fn
@@ -51,6 +52,7 @@
       ((matche-symbol-var? pat) pat)
       ((and (list? pat) (empty? pat)) (list (quote list)))
       ((list? pat) (cons (quote list) (map matche-pattern->expr pat)))
+      ((keyword? pat) pat)
       (:else (list (quote quote) pat)))))
 
 (define

lib/minikanren/tests/classics.sx

@@ -0,0 +1,87 @@
+;; lib/minikanren/tests/classics.sx — small classic-style puzzles that
+;; exercise the full system end to end (relations + conde + matche +
+;; fresh + run*). Each test is a self-contained miniKanren program.
+
+;; -----------------------------------------------------------------------
+;; Pet puzzle (3 friends, 3 pets, 1-each).
+;; -----------------------------------------------------------------------
+
+(mk-test
+  "classics-pet-puzzle"
+  (run*
+    q
+    (fresh
+      (a b c)
+      (== q (list a b c))
+      (permuteo (list :dog :cat :fish) (list a b c))
+      (== b :fish)
+      (conde ((== a :cat)) ((== a :fish)))))
+  (list (list :cat :fish :dog)))
+
+;; -----------------------------------------------------------------------
+;; Family-relations puzzle (uses membero on a fact list).
+;; -----------------------------------------------------------------------
+
+(define
+  parent-facts
+  (list
+    (list "alice" "bob")
+    (list "alice" "carol")
+    (list "bob" "dave")
+    (list "carol" "eve")
+    (list "dave" "frank")))
+
+(define parento (fn (x y) (membero (list x y) parent-facts)))
+
+(define grandparento (fn (x z) (fresh (y) (parento x y) (parento y z))))
+
+(mk-test
+  "classics-grandparents-of-frank"
+  (run* q (grandparento q "frank"))
+  (list "bob"))
+
+(mk-test
+  "classics-grandchildren-of-alice"
+  (run* q (grandparento "alice" q))
+  (list "dave" "eve"))
+
+;; -----------------------------------------------------------------------
+;; Symbolic differentiation, matche-driven.
+;;   Variable :x:                d/dx x  = 1
+;;   Sum (:+ a b):                d/dx (a+b) = (da + db)
+;;   Product (:* a b):            d/dx (a*b) = (da*b + a*db)
+;; -----------------------------------------------------------------------
+
+(define
+  diffo
+  (fn
+    (expr var d)
+    (matche
+      expr
+      (:x (== d 1))
+      ((:+ a b)
+        (fresh
+          (da db)
+          (== d (list :+ da db))
+          (diffo a var da)
+          (diffo b var db)))
+      ((:* a b)
+        (fresh
+          (da db)
+          (== d (list :+ (list :* da b) (list :* a db)))
+          (diffo a var da)
+          (diffo b var db))))))
+
+(mk-test "classics-diff-of-x" (run* q (diffo :x :x q)) (list 1))
+
+(mk-test
+  "classics-diff-of-x-plus-x"
+  (run* q (diffo (list :+ :x :x) :x q))
+  (list (list :+ 1 1)))
+
+(mk-test
+  "classics-diff-of-x-times-x"
+  (run* q (diffo (list :* :x :x) :x q))
+  (list (list :+ (list :* 1 :x) (list :* :x 1))))
+
+(mk-tests-run!)

plans/minikanren-on-sx.md

@@ -166,6 +166,13 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-08** — **Classic puzzles + matche keyword fix**: matche now emits
+  keywords bare in the pattern->expr conversion so they self-evaluate to their
+  string name and unify with the same-keyword target value (instead of becoming
+  a quoted-keyword type). New `tests/classics.sx`: pet permutation puzzle,
+  parent/grandparent inference over a fact list, symbolic differentiation
+  driven by matche dispatch on `:x` / `(:+ a b)` / `(:* a b)` patterns.
+  6 new tests, 228/228 cumulative.
 - **2026-05-08** — **Phase 5 piece D — matche, Phase 5 done**: pattern matching
   macro (`lib/minikanren/matche.sx`) — symbols become fresh vars, atoms become
   literals, lists recurse positionally, repeated names unify. 14 new tests