> You have to explicitly force the lazy value first- but other than it 
> being explicit, this is no different from other languages that 
> implicitly force the value for you.  Well, Haskell has an option where 
> a pattern match can always succeed that doesn't necessarily force the 
> lazy value (I forget what it's called at the moment), but baring that, 
> even standard Haskell pattern matching forces the value for the match.
...which is pretty much how it is going to have to work until someone 
builds a programming language with psychic precognition.

~~ Robert.