deferred evaulation of function calls

[Robert P. J. Day]

  can you distinguish between immediate and deferred function calls the 
way you can between immediate and deferred references to variables?  the
docs are confusing on this.  in section 4.4.1, "Wildcard Examples", there 
is an example of the "wildcard" function:

  objects := $(wildcard *.o)

the ":=" assignment seems to suggest that this is explicitly an immediate
assignment (a la variables).  but a quick test shows that using "=" seems
to produce the same effect.  so what's the difference when it comes to 
function calls?  the chapter on function calls doesn't address this, it
just launches into function examples.

rday