diff --git a/lib/guest/match.sx b/lib/guest/match.sx
new file mode 100644
index 00000000..8c1cb0c2
--- /dev/null
+++ b/lib/guest/match.sx
@@ -0,0 +1,185 @@
+;; lib/guest/match.sx — pure pattern-match + unification kit.
+;;
+;; Shipped for miniKanren / Datalog / future logic-flavoured guests that
+;; want immutable unification without writing it from scratch. The two
+;; existing prolog/haskell engines stay as-is — porting them in place
+;; risks the 746 tests they currently pass; consumers can migrate
+;; gradually via the converters in lib/guest/ast.sx.
+;;
+;; Term shapes (canonical wire format)
+;; -----------------------------------
+;;   var          (:var NAME)            NAME a string
+;;   constructor  (:ctor HEAD ARGS)      HEAD a string, ARGS a list of terms
+;;   literal      number / string / boolean / nil
+;;
+;; Guests with their own shape pass adapter callbacks via the cfg arg —
+;; see (unify-with cfg ...) and (match-pat-with cfg ...) below. The
+;; default canonical entry points (unify / match-pat) use the wire shape.
+;;
+;; Substitution / env
+;; ------------------
+;; A substitution is a SX dict mapping VAR-NAME → term. There are no
+;; trails, no mutation: each step either returns an extended dict or nil.
+;;
+;;   (empty-subst)                  → {}
+;;   (walk term s)                  → term with top-level vars resolved
+;;   (walk* term s)                 → term with all vars resolved (recursive)
+;;   (extend name term s)           → s with NAME → term added
+;;   (occurs? name term s)          → bool
+;;
+;; Unify (symmetric, miniKanren-flavour)
+;; -------------------------------------
+;;   (unify u v s)                  → extended subst or nil
+;;   (unify-with cfg u v s)         → ditto, with adapter callbacks:
+;;                                      :var? :var-name :ctor? :ctor-head
+;;                                      :ctor-args :occurs-check?
+;;
+;; Match (asymmetric, haskell-flavour: pattern → value, vars only in pat)
+;; ---------------------------------------------------------------------
+;;   (match-pat pat val env)        → extended env or nil
+;;   (match-pat-with cfg pat val env)
+
+(define mk-var  (fn (name) (list :var name)))
+(define mk-ctor (fn (head args) (list :ctor head args)))
+
+(define is-var?    (fn (t) (and (list? t) (not (empty? t)) (= (first t) :var))))
+(define is-ctor?   (fn (t) (and (list? t) (not (empty? t)) (= (first t) :ctor))))
+(define var-name   (fn (t) (nth t 1)))
+(define ctor-head  (fn (t) (nth t 1)))
+(define ctor-args  (fn (t) (nth t 2)))
+
+(define empty-subst (fn () {}))
+
+(define
+  walk
+  (fn (t s)
+    (if (and (is-var? t) (has-key? s (var-name t)))
+      (walk (get s (var-name t)) s)
+      t)))
+
+(define
+  walk*
+  (fn (t s)
+    (let ((w (walk t s)))
+      (cond
+        ((is-ctor? w)
+          (mk-ctor (ctor-head w) (map (fn (a) (walk* a s)) (ctor-args w))))
+        (:else w)))))
+
+(define
+  extend
+  (fn (name term s)
+    (assoc s name term)))
+
+(define
+  occurs?
+  (fn (name term s)
+    (let ((w (walk term s)))
+      (cond
+        ((is-var? w) (= (var-name w) name))
+        ((is-ctor? w) (some (fn (a) (occurs? name a s)) (ctor-args w)))
+        (:else false)))))
+
+(define
+  unify-with
+  (fn (cfg u v s)
+    (let ((var?-fn (get cfg :var?))
+          (var-name-fn (get cfg :var-name))
+          (ctor?-fn (get cfg :ctor?))
+          (ctor-head-fn (get cfg :ctor-head))
+          (ctor-args-fn (get cfg :ctor-args))
+          (occurs?-on (get cfg :occurs-check?)))
+      (let ((wu (walk-with cfg u s))
+            (wv (walk-with cfg v s)))
+        (cond
+          ((and (var?-fn wu) (var?-fn wv) (= (var-name-fn wu) (var-name-fn wv))) s)
+          ((var?-fn wu)
+            (if (and occurs?-on (occurs-with cfg (var-name-fn wu) wv s))
+              nil
+              (extend (var-name-fn wu) wv s)))
+          ((var?-fn wv)
+            (if (and occurs?-on (occurs-with cfg (var-name-fn wv) wu s))
+              nil
+              (extend (var-name-fn wv) wu s)))
+          ((and (ctor?-fn wu) (ctor?-fn wv))
+            (if (= (ctor-head-fn wu) (ctor-head-fn wv))
+              (unify-list-with
+                cfg
+                (ctor-args-fn wu)
+                (ctor-args-fn wv)
+                s)
+              nil))
+          (:else (if (= wu wv) s nil)))))))
+
+(define
+  walk-with
+  (fn (cfg t s)
+    (if (and ((get cfg :var?) t) (has-key? s ((get cfg :var-name) t)))
+      (walk-with cfg (get s ((get cfg :var-name) t)) s)
+      t)))
+
+(define
+  occurs-with
+  (fn (cfg name term s)
+    (let ((w (walk-with cfg term s)))
+      (cond
+        (((get cfg :var?) w) (= ((get cfg :var-name) w) name))
+        (((get cfg :ctor?) w)
+          (some (fn (a) (occurs-with cfg name a s)) ((get cfg :ctor-args) w)))
+        (:else false)))))
+
+(define
+  unify-list-with
+  (fn (cfg xs ys s)
+    (cond
+      ((and (empty? xs) (empty? ys)) s)
+      ((or (empty? xs) (empty? ys)) nil)
+      (:else
+        (let ((s2 (unify-with cfg (first xs) (first ys) s)))
+          (if (= s2 nil)
+            nil
+            (unify-list-with cfg (rest xs) (rest ys) s2)))))))
+
+(define canonical-cfg
+  {:var? is-var? :var-name var-name
+   :ctor? is-ctor? :ctor-head ctor-head :ctor-args ctor-args
+   :occurs-check? true})
+
+(define unify (fn (u v s) (unify-with canonical-cfg u v s)))
+
+;; Asymmetric pattern match (haskell-style): only patterns may contain vars;
+;; values are concrete. On a var pattern, bind name to value.
+(define
+  match-pat-with
+  (fn (cfg pat val env)
+    (let ((var?-fn (get cfg :var?))
+          (var-name-fn (get cfg :var-name))
+          (ctor?-fn (get cfg :ctor?))
+          (ctor-head-fn (get cfg :ctor-head))
+          (ctor-args-fn (get cfg :ctor-args)))
+      (cond
+        ((var?-fn pat) (extend (var-name-fn pat) val env))
+        ((and (ctor?-fn pat) (ctor?-fn val))
+          (if (= (ctor-head-fn pat) (ctor-head-fn val))
+            (match-list-pat-with
+              cfg
+              (ctor-args-fn pat)
+              (ctor-args-fn val)
+              env)
+            nil))
+        ((ctor?-fn pat) nil)
+        (:else (if (= pat val) env nil))))))
+
+(define
+  match-list-pat-with
+  (fn (cfg pats vals env)
+    (cond
+      ((and (empty? pats) (empty? vals)) env)
+      ((or (empty? pats) (empty? vals)) nil)
+      (:else
+        (let ((env2 (match-pat-with cfg (first pats) (first vals) env)))
+          (if (= env2 nil)
+            nil
+            (match-list-pat-with cfg (rest pats) (rest vals) env2)))))))
+
+(define match-pat (fn (pat val env) (match-pat-with canonical-cfg pat val env)))
diff --git a/lib/guest/tests/match.sx b/lib/guest/tests/match.sx
new file mode 100644
index 00000000..25eb3a7b
--- /dev/null
+++ b/lib/guest/tests/match.sx
@@ -0,0 +1,108 @@
+;; lib/guest/tests/match.sx — exercises lib/guest/match.sx.
+
+(define gmatch-test-pass 0)
+(define gmatch-test-fail 0)
+(define gmatch-test-fails (list))
+
+(define
+  gmatch-test
+  (fn (name actual expected)
+    (if (= actual expected)
+      (set! gmatch-test-pass (+ gmatch-test-pass 1))
+      (begin
+        (set! gmatch-test-fail (+ gmatch-test-fail 1))
+        (append! gmatch-test-fails {:name name :expected expected :actual actual})))))
+
+;; ── walk / extend / occurs ────────────────────────────────────────
+(gmatch-test "walk-direct"
+  (walk (mk-var "x") (extend "x" 5 (empty-subst))) 5)
+
+(gmatch-test "walk-chain"
+  (walk (mk-var "a") (extend "a" (mk-var "b") (extend "b" 7 (empty-subst)))) 7)
+
+(gmatch-test "walk-no-binding"
+  (let ((v (mk-var "u"))) (= (walk v (empty-subst)) v)) true)
+
+(gmatch-test "walk*-recursive"
+  (walk* (mk-ctor "Just" (list (mk-var "x"))) (extend "x" 9 (empty-subst)))
+  (mk-ctor "Just" (list 9)))
+
+(gmatch-test "occurs-direct"
+  (occurs? "x" (mk-var "x") (empty-subst)) true)
+
+(gmatch-test "occurs-nested"
+  (occurs? "x" (mk-ctor "f" (list (mk-var "x"))) (empty-subst)) true)
+
+(gmatch-test "occurs-not"
+  (occurs? "x" (mk-var "y") (empty-subst)) false)
+
+;; ── unify (symmetric) ─────────────────────────────────────────────
+(gmatch-test "unify-equal-literals"
+  (len (unify 5 5 (empty-subst))) 0)
+
+(gmatch-test "unify-different-literals"
+  (unify 5 6 (empty-subst)) nil)
+
+(gmatch-test "unify-var-literal"
+  (get (unify (mk-var "x") 5 (empty-subst)) "x") 5)
+
+(gmatch-test "unify-literal-var"
+  (get (unify 5 (mk-var "x") (empty-subst)) "x") 5)
+
+(gmatch-test "unify-same-var"
+  (len (unify (mk-var "x") (mk-var "x") (empty-subst))) 0)
+
+(gmatch-test "unify-two-vars"
+  (let ((s (unify (mk-var "x") (mk-var "y") (empty-subst))))
+    (or (= (get s "x") (mk-var "y")) (= (get s "y") (mk-var "x")))) true)
+
+(gmatch-test "unify-ctor-equal"
+  (len (unify (mk-ctor "f" (list 1 2)) (mk-ctor "f" (list 1 2)) (empty-subst))) 0)
+
+(gmatch-test "unify-ctor-with-var"
+  (get (unify (mk-ctor "Just" (list (mk-var "x"))) (mk-ctor "Just" (list 7)) (empty-subst)) "x") 7)
+
+(gmatch-test "unify-ctor-head-mismatch"
+  (unify (mk-ctor "Just" (list 1)) (mk-ctor "Nothing" (list)) (empty-subst)) nil)
+
+(gmatch-test "unify-ctor-arity-mismatch"
+  (unify (mk-ctor "f" (list 1 2)) (mk-ctor "f" (list 1)) (empty-subst)) nil)
+
+(gmatch-test "unify-occurs-check"
+  (unify (mk-var "x") (mk-ctor "f" (list (mk-var "x"))) (empty-subst)) nil)
+
+(gmatch-test "unify-transitive-vars"
+  (let ((s (unify (mk-var "x") (mk-var "y") (empty-subst))))
+    (let ((s2 (unify (mk-var "y") 42 s)))
+      (walk (mk-var "x") s2))) 42)
+
+;; ── match-pat (asymmetric) ────────────────────────────────────────
+(gmatch-test "match-var-binds"
+  (get (match-pat (mk-var "x") 99 (empty-subst)) "x") 99)
+
+(gmatch-test "match-literal-equal"
+  (len (match-pat 5 5 (empty-subst))) 0)
+
+(gmatch-test "match-literal-mismatch"
+  (match-pat 5 6 (empty-subst)) nil)
+
+(gmatch-test "match-ctor-binds"
+  (get (match-pat (mk-ctor "Just" (list (mk-var "y")))
+                  (mk-ctor "Just" (list 11))
+                  (empty-subst)) "y") 11)
+
+(gmatch-test "match-ctor-head-mismatch"
+  (match-pat (mk-ctor "Just" (list (mk-var "y")))
+             (mk-ctor "Nothing" (list))
+             (empty-subst)) nil)
+
+(gmatch-test "match-ctor-arity-mismatch"
+  (match-pat (mk-ctor "f" (list (mk-var "x") (mk-var "y")))
+             (mk-ctor "f" (list 1))
+             (empty-subst)) nil)
+
+(define gmatch-tests-run!
+  (fn ()
+    {:passed gmatch-test-pass
+     :failed gmatch-test-fail
+     :total  (+ gmatch-test-pass gmatch-test-fail)}))