Re: Optional types

[Dan Weinreb <address@hidden>]

   Date: Thu, 6 Dec 2001 17:07:25 -0400
   From: shivers@cc.gatech.edu

   One problem with this idea of "optional type declarations" is that crossing
   from a dynamically-typed world into a declared-type world can be quite
   expensive. 

Even without crossing worlds, this issue comes up if you are casting
an expression declared to be "UrType" to type "List-o'-Strings".  It's
a special case of the general problem of the cost of running assertion
predicates, since exactly the same issue comes up if you want to check
something that the type-declaration-langauge can't express.  So I think
this is just a special case of an issue that would even arise in a
language with no type declarations at all.