CTFE vs. traditional metaprogramming

[language_fan]

Sat, 10 Oct 2009 10:30:31 +0200, Don thusly wrote:

> The more fundamental problem is that you can't
> instantiate a template from inside CTFE. IE, you can cross from the
> "compile-time world" to the "runtime world" only once -- you can never
> get back.

That's not exactly true. Also both templates and CTFE are compile time 
features. You can compute a value with CTFE in the "value world" and lift 
the result to the "type world" with a template. The range of a template 
used as a metafunction is {types, values} and their mixture. CTFE 
functions only return values.  Understanding the concept of 'lambda cube' 
will help you here.