[Types-sig] how to do a typecase? (was: Static typing: Towards closure?)

Jeremy Hylton jeremy@cnri.reston.va.us
Fri, 21 Jan 2000 12:19:29 -0500 (EST)

>>>>> "GvR" == Guido van Rossum <guido@CNRI.Reston.VA.US> writes:

  GvR> True, this is always a risk when you have multiple
  GvR> implementations of the same set of complex rules, but we
  GvR> shouldn't build this attitude into our definition of the
  GvR> typechecker.

Absolutely!  The rules may be complex but they should be stated
precisely and unambiguously.  The implementation of the type checker
will be complex, so we need these rules to verify the correctness of
the type checker.  If a program checks out with one implementation and
not with another, then one of the type checkers has a bug!