[racket] constructing a boolean that's a filter for a given type? could be automatic?

On Jan 30, 2012, at 6:00 PM, John Clements wrote:

> 
> On Jan 30, 2012, at 1:14 PM, Matthias Felleisen wrote:
> 
>> 
>> On Jan 30, 2012, at 4:11 PM, Sam Tobin-Hochstadt wrote:
>> 
>>> Perhaps it should just have less information.
>> 
>> 
>> I like that a lot. 
> 
> I'm not sure I do; if I were on a desert island or had just kicked Sam in the shin yesterday, I'd probably want to examine this type carefully to see whether I could interpret it and whether it actually looked like it should be equivalent to a filter for the type that I wanted.  At a minimum, I'd like to know that the information is available. I realize this is like Guillaume's syntax-errors-for-beginners discussion, but I don't think I reach the same conclusion


This is precisely correct. Just as in the general types case, make information available on demand not immediately. Lazy lazy über alles.