--- a/python/c3/typecheck.py	Fri May 24 20:45:03 2013 +0200
+++ b/python/c3/typecheck.py	Sat May 25 14:26:25 2013 +0200
@@ -13,8 +13,14 @@
    def __init__(self, diag):
       self.diag = diag
       self.visitor = Visitor(self.precheck, self.check2)
+   def error(self, msg, loc):
+        """ Wrapper that registers the message and marks the result invalid """
+        self.diag.error(msg, loc)
+        self.ok = False
    def checkPackage(self, pkg):
-      self.visitor.visit(pkg)
+        self.ok = True
+        self.visitor.visit(pkg)
+        return self.ok
    def precheck(self, sym):
       pass
    def check2(self, sym):
@@ -22,10 +28,10 @@
          pass
       elif type(sym) in [IfStatement, WhileStatement]:
          if not equalTypes(sym.condition.typ, boolType):
-            self.diag.error('Condition must be of type {0}'.format(boolType), sym.condition.loc)
+            self.error('Condition must be of type {0}'.format(boolType), sym.condition.loc)
       elif type(sym) is Assignment:
          if not equalTypes(sym.lval.typ, sym.rval.typ):
-            self.diag.error('Cannot assign {0} to {1}'.format(sym.rval.typ, sym.lval.typ), sym.loc)
+            self.error('Cannot assign {0} to {1}'.format(sym.rval.typ, sym.lval.typ), sym.loc)
       elif type(sym) is ReturnStatement:
          pass
       elif type(sym) is FunctionCall:
@@ -35,11 +41,11 @@
             ptypes = sym.proc.typ.parametertypes
             nreq = len(ptypes)
             if ngiv != nreq:
-               self.diag.error('Function {2}: {0} arguments required, {1} given'.format(nreq, ngiv, sym.proc.name), sym.loc)
+               self.error('Function {2}: {0} arguments required, {1} given'.format(nreq, ngiv, sym.proc.name), sym.loc)
             else:
                for a, at in zip(sym.args, ptypes):
                   if not equalTypes(a.typ, at):
-                     self.diag.error('Got {0}, expected {1}'.format(a.typ, at), a.loc)
+                     self.error('Got {0}, expected {1}'.format(a.typ, at), a.loc)
             # determine return type:
             sym.typ = sym.proc.typ.returntype
          else:
@@ -57,29 +63,29 @@
          elif type(sym.val) is bool:
             sym.typ = boolType
          else:
-            self.diag.error('Unknown literal type', sym.loc)
+            self.error('Unknown literal type', sym.loc)
       elif type(sym) is Binop:
          if sym.op in ['+', '-', '*', '/']:
             if equalTypes(sym.a.typ, sym.b.typ):
                if equalTypes(sym.a.typ, intType):
                   sym.typ = sym.a.typ
                else:
-                  self.diag.error('Can only add integers', sym.loc)
+                  self.error('Can only add integers', sym.loc)
                   sym.typ = intType
             else:
                # assume void here? TODO: throw exception!
                sym.typ = intType
-               self.diag.error('Types unequal', sym.loc)
+               self.error('Types unequal', sym.loc)
          elif sym.op in ['>', '<', '==', '<=', '>=']:
             sym.typ = boolType
             if not equalTypes(sym.a.typ, sym.b.typ):
-               self.diag.error('Types unequal', sym.loc)
+               self.error('Types unequal', sym.loc)
          elif sym.op in ['or', 'and']:
             sym.typ = boolType
             if not equalTypes(sym.a.typ, boolType):
-               self.diag.error('Must be {0}'.format(boolType), sym.a.loc)
+               self.error('Must be {0}'.format(boolType), sym.a.loc)
             if not equalTypes(sym.b.typ, boolType):
-               self.diag.error('Must be {0}'.format(boolType), sym.b.loc)
+               self.error('Must be {0}'.format(boolType), sym.b.loc)
          else:
             sym.typ = voidType
             print('unknown binop', sym.op)
@@ -89,10 +95,10 @@
          pass
       elif type(sym) is Constant:
          if not equalTypes(sym.typ, sym.value.typ):
-            self.diag.error('Cannot assign {0} to {1}'.format(sym.value.typ, sym.typ), sym.loc)
+            self.error('Cannot assign {0} to {1}'.format(sym.value.typ, sym.typ), sym.loc)
          
       elif type(sym) in [EmptyStatement, CompoundStatement, Package, Function, FunctionType]:
          pass
       else:
-         print('Unknown type check', sym)
+            raise Exception('Unknown type check {0}'.format(sym))