About thunks; this is actually a situation where statically typed languages have the potential to do something interesting that is hard in dynamically typed systems.
If foo takes an argument that should be a zero arity function that returns a number, and you write:
(foo (+ x y))
The compiler could recognize that the expression you used for the argument can be converted into a function with the correct signature. I think I have heard of languages on the JVM that do this, not sure which.
Also note that Smalltalk-80 is very much designed around the principle of thunks. E.g:
