question about 'mixed' tuples

[Lutger]

I have some troubles finding out what one can do with tuples that 
consist of both types and expressions. I would like, for example, to 
create a type tuple out of a mixed tuple.

Take this example from the article on digitalmars:

alias Tuple!(float, float, 3) TP;
TP.length	// evaluates to 3

TP.length however gives me a compiler error: 'float is not an expression'

It works nicely if TP is a tuple of only types or expressions, but not 
for mixed tuples.

Am I doing something wrong, or is this not possible?