diff --git a/csp/domain.rkt b/csp/domain.rkt
index a9063e6f..a04b7db8 100644
--- a/csp/domain.rkt
+++ b/csp/domain.rkt
@@ -2,18 +2,11 @@
 (require racket/class racket/list "helper.rkt")
 (provide (all-defined-out))
 
-(define proc<%>
-  (interface* ()
-              ([prop:procedure
-                (λ(this)
-                  (send this get-values))])
-              get-values))
-
 ;; Class used to control possible values for variables
 ;; When list or tuples are used as domains, they are automatically
 ;; converted to an instance of that class.
 (define domain%  
-  (class* object% (printable<%> proc<%>)
+  (class* object% (printable<%> (make-proc<%> get-values))
     (super-new)
     (init-field set)
     (field [_list set][_hidden null][_states null])
diff --git a/csp/helper.rkt b/csp/helper.rkt
index ffb993ce..71bc942f 100644
--- a/csp/helper.rkt
+++ b/csp/helper.rkt
@@ -1,8 +1,15 @@
 #lang racket/base
-(require racket/list)
+(require racket/class racket/list (for-syntax racket/base racket/syntax))
 (provide (all-defined-out))
 (require rackunit)
 
+(define-syntax-rule (make-proc<%> proc-name)
+  (interface* ()
+              ([prop:procedure
+                (λ(this . args)
+                  (send/apply this proc-name args))])
+              proc-name))
+
 (define-simple-check (check-hash-items h1 h2)
   (for/and ([(k1 v1) (in-hash h1)])
     (equal? (hash-ref h2 k1) v1)))