--- a/python/libasm.py	Fri May 31 21:06:44 2013 +0200
+++ b/python/libasm.py	Sat Jun 01 11:55:49 2013 +0200
@@ -1,6 +1,8 @@
 import re
 import pyyacc
 from ppci import Token, CompilerError, SourceLocation
+import sys, argparse
+
 
 # Different instruction sets:
 class InstructionSet:
@@ -98,8 +100,10 @@
 
 class AExpression(ANode):
     def __add__(self, other):
+        assert isinstance(other, AExpression)
         return ABinop('+', self, other)
     def __mul__(self, other):
+        assert isinstance(other, AExpression)
         return ABinop('*', self, other)
 
 class ABinop(AExpression):
@@ -138,6 +142,7 @@
         g.add_production('asmline', ['label', 'instruction'])
         g.add_production('asmline', ['instruction'])
         g.add_production('asmline', ['label'])
+        g.add_production('asmline', [])
         g.add_production('label', ['ID', ':'], self.p_label)
         g.add_production('instruction', ['opcode', 'operands'], self.p_ins_1)
         g.add_production('instruction', ['opcode'], self.p_ins_2)
@@ -186,33 +191,47 @@
         n = int(n)
         return ANumber(n)
 
-    # Top level:
+    # Top level interface:
     def emit(self, a):
+        """ Emit a parsed instruction """
         self.output.append(a)
+        # Determine the bit pattern from a lookup table:
+        # TODO
+
 
     def parse_line(self, line):
         """ Parse line into asm AST """
         tokens = tokenize(line)
         self.p.parse(tokens)
-        aast = 1 # TODO
-        return aast
 
     def assemble(self, asmsrc):
-        lxr = Lexer(asmsrc)
-        prsr = Parser(lxr)
-        instructions = prsr.parse()
-        return instructions
+        """ Assemble this source snippet """
+        for line in asmsrc.split('\n'):
+            self.assemble_line(line)
+        self.back_patch()
 
-    def assembleLine(self, line):
+    def assemble_line(self, line):
         """ 
             Assemble a single source line. 
             Do not take newlines into account 
         """
-        aast = self.parseLine(line)
-        self.assemble_aast(aast)
+        self.parse_line(line)
+        self.assemble_aast()
 
     def assemble_aast(self, at):
         """ Assemble a parsed asm line """
         pass
 
+    def back_patch(self):
+        """ Fix references to earlier labels """
+        pass
 
+
+if __name__ == '__main__':
+    # When run as main file, try to grab command line arguments:
+    parser = argparse.ArgumentParser(description="Assembler")
+    parser.add_argument('sourcefile', type=argparse.FileType('r'), help='the source file to assemble')
+    args = parser.parse_args()
+    a = Assembler()
+    obj = a.assemble(args.sourcefile.read())
+