report line and column number on parsing error

parser/Parser.py

@@ -1,4 +1,5 @@
 
+import sys
 import ply.yacc as yacc
 from Lexer import Lexer
 from nodes import *
@@ -48,6 +49,9 @@ class Parser(object):
 
     def p_error(self, p):
         self.saw_error = True
+        col = p.lexpos - max(0, self.input.rfind('\n', 0, p.lexpos))
+        sys.stdout.write('Error: Unexpected %s at line %d, col %d\n' % (
+                p.type, p.lineno, col))
 
     def parse(self):
         return self.parser.parse(self.input, lexer = self.lexer)