--- a/python/target.py	Sun Jun 09 16:06:49 2013 +0200
+++ b/python/target.py	Thu Jun 13 00:07:28 2013 +0200
@@ -15,14 +15,21 @@
         self.name = name
 
 class Instruction:
-   def __init__(self, opcode):
-      self.opcode = opcode
+    def encode(self):
+        raise NotImplementedError('TODO')
 
 class Target:
-    def __init__(self):
+    def __init__(self, name, desc=''):
+        self.name = name
+        self.desc = desc
         self.registers = []
         self.instructions = []
 
+    def instruction(self, cls):
+        """ Decorator function that registers an instruction to this target """
+        self.instructions.append(cls)
+        return cls
+
     def mapOperand(self, operand):
         """ Try to map an operand to a target type """
         if type(operand) is ASymbol:
@@ -32,8 +39,7 @@
                 regs[r.name] = r
             if operand.name in regs:
                 return regs[operand.name]
-        else:
-            return
+        raise CompilerError('Cannot map {0}'.format(operand))
 
     def mapInstruction(self, vi):
         """ Map ast tree to real instruction for this target """
@@ -47,5 +53,5 @@
             if ic.mnemonic == vi.opcode and ic.operands == optypes:
                 ri = ic(*rops)
                 return ri
-        raise CompilerError('No suitable instruction found')
+        raise CompilerError('No suitable instruction found for "{0}"'.format(vi))