diff --git a/hygiene.zp b/hygiene.zp
new file mode 100644
index 0000000..b8e325b
--- /dev/null
+++ b/hygiene.zp
@@ -0,0 +1,69 @@
+(define-struct syntax (e scopes))
+
+(define (identifier? s) (syntax:syntax? s))
+
+(define (datum->syntax v)
+  (cond
+    ((syntax:syntax? v) v)
+    ((symbol? v) (syntax:make-syntax v []))
+    ((list? v) (map datum->syntax v))
+    (else v)))
+
+(define (syntax->datum s)
+  (cond
+    ((syntax:syntax? s) (syntax:get-e s))
+    ((list? s) (map syntax->datum s))
+    (else s)))
+
+(defimpl stringify syntax:syntax?
+  ((->string (lambda (v)
+    (++ "(syntax "
+        (->string (syntax:get-e v))
+        " "
+        (->string (syntax:get-scopes v))
+        ")")))))
+
+(write (->string (datum->syntax '(a b c))))
+(write (->string (syntax->datum (datum->syntax '(a b c)))))
+
+(define-struct scope (id))
+
+(define ID 0)
+
+(defimpl stringify scope:scope?
+  ((->string (lambda (v)
+    (++ "(scope "
+        (->string (scope:get-id v))
+        ")")))))
+
+(define (scope:new-scope)
+  (begin
+    (set! ID (+ ID 1))
+    (scope:make-scope ID)))
+
+(define (adjust-scope s sc op)
+  (cond
+    ((syntax:syntax? s) (syntax:make-syntax (syntax:get-e s)
+                                            (op (syntax:get-scopes s) sc)))
+    ((list? s) (map ($ (adjust-scope % sc op)) s))
+    (else s)))
+
+(define (add-scope s sc)
+  (adjust-scope s sc ++))
+
+(define (flip-scope s sc)
+  (adjust-scope s sc set-flip))
+
+(define (set-flip s e)
+  (if (in? s e)
+    (filter ($ (/= (scope:get-id %) (scope:get-id e))) s)
+    (++ s e)))
+
+(write (->string (add-scope (datum->syntax '(a b c)) (scope:new-scope))))
+(let ((s (scope:new-scope)))
+  (write (->string (flip-scope (add-scope (datum->syntax 'a) s) s))))
+
+(define all-bindings #{})
+
+(define (add-binding! id binding)
+  (hash:set! all-bindings id binding))