Parallel-safe lambdas

[Mark Thornton]

John Rose wrote:
>  4. allow unqualified references to uplevel methods if they are "pure" (marked @Pure)
>   
A colleague recently suggested that a parameter to one of my methods 
needed to be marked as @Pure. The parameter was a single method 
interface, where the method would be called an indeterminate number of 
times and must return the same value on each occasion without side 
effects. The usage in this case wasn't necessarily concurrent.

Mark