diff --git a/wip-duuqnd/compiler.lisp b/wip-duuqnd/compiler.lisp
index 415c672..66926ea 100644
--- a/wip-duuqnd/compiler.lisp
+++ b/wip-duuqnd/compiler.lisp
@@ -1,7 +1,8 @@
-(defpackage #:compiler
+(defpackage #:user-side-compiler
+  (:nicknames #:usc)
   (:use #:cl))
 
-(in-package #:compiler)
+(in-package #:user-side-compiler)
 
 (defvar *label-counter* 0)
 
@@ -13,9 +14,14 @@
 
 (defclass reference () ())
 
+(defgeneric ref-constantp (reference) (:method (reference) nil))
+
 (defclass reference-constant (reference)
   ((%value :accessor ref-value :initarg :value)))
 
+(defmethod ref-constantp ((reference reference-constant))
+  t)
+
 (defmethod print-object ((object reference-constant) stream)
   (print-unreadable-object (object stream :type t)
     (format stream "~D" (ref-value object))))
@@ -34,7 +40,6 @@
   (format-inst t "LDY #~D" (ref-index ref))
   (format-inst t "LDA VARVEC,Y"))
 
-
 (defclass node ()
   ((%next :accessor next :accessor normal-next :initform nil)))
 
diff --git a/wip-duuqnd/instruction-list.txt b/wip-duuqnd/instruction-list.txt
new file mode 100644
index 0000000..0ff29c8
Binary files /dev/null and b/wip-duuqnd/instruction-list.txt differ
diff --git a/wip-duuqnd/instruction.lisp b/wip-duuqnd/instruction.lisp
new file mode 100644
index 0000000..ba20b59
--- /dev/null
+++ b/wip-duuqnd/instruction.lisp
@@ -0,0 +1,54 @@
+(in-package #:user-side-compiler)
+
+(defgeneric check-arguments (instruction))
+
+(defclass instruction ()
+  ((%mnemonic :allocation :class :reader mnemonic :initarg :mnemonic)
+   (%operand :accessor operand :initarg :operand)
+   (%next :accessor next :accessor normal-next :initarg :next)))
+
+(defclass complete-mixin ()
+  ((%opcode :allocation :class :reader opcode :initarg :opcode)))
+
+(defclass immediate-mixin () ())
+(defclass implied-mixin () ())
+(defclass zero-page-mixin () ())
+(defclass zero-page-x-mixin (zero-page-mixin) ())
+(defclass absolute-mixin () ())
+(defclass absolute-x-mixin (absolute-mixin) ())
+(defclass absolute-y-mixin (absolute-mixin) ())
+(defclass indirect-x-mixin (zero-page-mixin) ())
+(defclass indirect-y-mixin (zero-page-mixin) ())
+
+(defun addressing-mode-to-class-name (mode-keyword)
+  (cadr (assoc mode-keyword
+               '((:implied implied-mixin)
+                 (:immediate immediate-mixin)
+                 (:zero-page zero-page-mixin)
+                 (:zero-page-x zero-page-x-mixin)
+                 (:zero-page-y zero-page-y-mixin)
+                 (:absolute absolute-mixin)
+                 (:absolute-x absolute-x-mixin)
+                 (:absolute-y absolute-y-mixin)
+                 (:indirect-x indirect-x-mixin)
+                 (:indirect-y indirect-y-mixin)))))
+
+(defclass branching-mixin ()
+  ((%branch-next :accessor branch-next :initarg :branch-next)))
+
+(defmacro define-instruction (mnemonic branching-p &rest modes-and-codes)
+  (let* ((name (string-upcase mnemonic))
+         (base-name (intern (format nil "INST-~A" name))))
+    `(progn
+       (defclass ,base-name (instruction)
+         ((%mnemonic :allocation :class :initform ',mnemonic)))
+       ,@(loop :for (mode code) :in modes-and-codes
+               :collect `(defclass ,(intern (format nil "INST-~A-~A"
+                                                    name mode))
+                             ,(append
+                               `(,base-name
+                                 ,(addressing-mode-to-class-name mode)
+                                 complete-mixin)
+                               (when branching-p
+                                 '(branching-mixin)))
+                           ((%opcode :allocation :class :initform ,code)))))))