Simplify and improve Emitter abstraction.

src/sixtypical/compiler.py

@@ -9,7 +9,7 @@ from sixtypical.model import (
     TableType, PointerType, RoutineType, VectorType,
     REG_A, REG_X, REG_Y, FLAG_C
 )
-from sixtypical.emitter import Byte, Word, Table, Label, Offset, LowAddressByte, HighAddressByte, Emitter
+from sixtypical.emitter import Byte, Word, Table, Label, Offset, LowAddressByte, HighAddressByte
 from sixtypical.gen6502 import (
     Immediate, Absolute, AbsoluteX, AbsoluteY, ZeroPage, Indirect, IndirectY, Relative,
     LDA, LDX, LDY, STA, STX, STY,
@@ -160,15 +160,13 @@ class Compiler(object):
         assert isinstance(routine, Routine)
 
         self.current_routine = routine
-        saved_emitter = self.emitter
-        self.emitter = Emitter(saved_emitter.addr)
+
         if routine.block:
             self.emitter.resolve_label(self.get_label(routine.name))
             self.compile_block(routine.block)
 
             needs_rts = True
-            if self.emitter.accum:
-                last_op = self.emitter.accum[-1]
+            last_op = self.emitter.get_tail()
             if isinstance(last_op, JMP):
                 needs_rts = False
                 if isinstance(last_op.operand, Absolute):
@@ -179,8 +177,6 @@ class Compiler(object):
             if needs_rts:
                 self.emitter.emit(RTS())
 
-        saved_emitter.emit(*self.emitter.accum)
-        self.emitter = saved_emitter
         self.current_routine = None
 
     def compile_block(self, block):

src/sixtypical/emitter.py

@@ -171,6 +171,12 @@ class Emitter(object):
             self.accum.append(thing)
             self.addr += thing.size()
 
+    def get_tail(self):
+        if self.accum:
+            return self.accum[-1]
+        else:
+            return None
+
     def retract(self):
         thing = self.accum.pop()
         self.addr -= thing.size()