pytholite/compiler: SymbolStack

diff --git a/migen/pytholite/compiler.py b/migen/pytholite/compiler.py
index 14fb248b59141667f2fc4e77ae621b5d10a2a82b..28fe19be55d98fbd05440465913e7b8a2e92b77b 100644 (file)
--- a/migen/pytholite/compiler.py
+++ b/migen/pytholite/compiler.py
@@ -55,13 +55,35 @@ class _Register:
                sync = [Case(self.sel, *cases)]
                return Fragment(sync=sync)
 
+class _SymbolStack:
+       def __init__(self):
+               self.stack = []
+       
+       def push(self, init={}):
+               self.stack.append(init)
+       
+       def pop(self):
+               return self.stack.pop()
+       
+       def __setitem__(self, key, value):
+               self.stack[-1][key] = value
+       
+       def __getitem__(self, key):
+               for frame in reversed(self.stack):
+                       try:
+                               return frame[key]
+                       except KeyError:
+                               pass
+               raise KeyError
+               
 class _AbstractNextState:
        def __init__(self, target_state):
                self.target_state = target_state
 
 class _Compiler:
        def __init__(self, symdict, registers):
-               self.symdict = symdict
+               self.symdict = _SymbolStack()
+               self.symdict.push(symdict)
                self.registers = registers
                self.targetname = ""