mk: phase 5D — matche pattern matching, phase 5 complete

Pattern grammar: _, symbol, atom (number/string/keyword/bool), (), and
(p1 ... pn) list patterns (recursive). Symbols become fresh vars in a
fresh form, atoms become literals to unify against, lists recurse
position-wise. Repeated names produce the same fresh var (so they
unify by ==).

Macro is built with explicit cons/list rather than a quasiquote because
the quasiquote expander does not recurse into nested lambda bodies —
the natural `\`(matche-clause (quote ,target) cl)` spelling left
literal `(unquote target)` forms in the output.

14 tests, 222/222 cumulative. Phase 5 done (project, conda, condu,
onceo, nafc, matche all green).

lib/minikanren/tests/matche.sx

@@ -0,0 +1,138 @@
+;; lib/minikanren/tests/matche.sx — Phase 5 piece D tests for `matche`.
+
+;; --- literal patterns ---
+
+(mk-test
+  "matche-literal-number"
+  (run* q (matche q (1 (== q 1))))
+  (list 1))
+
+(mk-test
+  "matche-literal-string"
+  (run* q (matche q ("hello" (== q "hello"))))
+  (list "hello"))
+
+(mk-test
+  "matche-literal-no-clause-matches"
+  (run*
+    q
+    (matche 7 (1 (== q :a)) (2 (== q :b))))
+  (list))
+
+;; --- variable patterns ---
+
+(mk-test
+  "matche-symbol-pattern"
+  (run* q (fresh (x) (== x 99) (matche x (a (== q a)))))
+  (list 99))
+
+(mk-test
+  "matche-wildcard"
+  (run* q (fresh (x) (== x 7) (matche x (_ (== q :any)))))
+  (list :any))
+
+;; --- list patterns ---
+
+(mk-test
+  "matche-empty-list"
+  (run* q (matche (list) (() (== q :ok))))
+  (list :ok))
+
+(mk-test
+  "matche-pair-binds"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 1 2))
+      (matche x ((a b) (== q (list b a))))))
+  (list (list 2 1)))
+
+(mk-test
+  "matche-triple-binds"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 1 2 3))
+      (matche x ((a b c) (== q (list :sum a b c))))))
+  (list (list :sum 1 2 3)))
+
+(mk-test
+  "matche-mixed-literal-and-var"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 1 99 3))
+      (matche x ((1 m 3) (== q m)))))
+  (list 99))
+
+;; --- multi-clause dispatch ---
+
+(mk-test
+  "matche-multi-clause-shape"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 5 6))
+      (matche
+        x
+        (() (== q :empty))
+        ((a) (== q (list :one a)))
+        ((a b) (== q (list :two a b))))))
+  (list (list :two 5 6)))
+
+(mk-test
+  "matche-three-shapes-via-fresh"
+  (run*
+    q
+    (fresh
+      (x)
+      (matche
+        x
+        (() (== q :empty))
+        ((a) (== q (list :one a)))
+        ((a b) (== q (list :two a b))))))
+  (list
+    :empty (list :one (make-symbol "_.0"))
+    (list :two (make-symbol "_.0") (make-symbol "_.1"))))
+
+;; --- nested patterns ---
+
+(mk-test
+  "matche-nested"
+  (run*
+    q
+    (fresh
+      (x)
+      (==
+        x
+        (list (list 1 2) (list 3 4)))
+      (matche x (((a b) (c d)) (== q (list a b c d))))))
+  (list (list 1 2 3 4)))
+
+;; --- repeated var names create the same fresh var → must unify ---
+
+(mk-test
+  "matche-repeated-var-implies-equality"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 7 7))
+      (matche x ((a a) (== q a)))))
+  (list 7))
+
+(mk-test
+  "matche-repeated-var-mismatch-fails"
+  (run*
+    q
+    (fresh
+      (x)
+      (== x (list 7 8))
+      (matche x ((a a) (== q a)))))
+  (list))
+
+(mk-tests-run!)