Thanks for the replies.

Yeah, I surely preferred simple configuration. I just wish that
with if we can organize compares and processes into a tree
to accelerate the processing. I kind of like the idea of "if". It
make nginx more powerful and flexible.

And I also noticed the overhead of context and script engine.
I have not figured out whether these overheads will consume
the processing time "tree like if" have saved. I'll do more tests.
Also the try_files which I have ignored. Thanks Merlin.

Maybe the context overhead is necessary. But the compare
result can be cached. lighttpd have such mechanism.

BTW,
I didn't quite follow Igor. Will "if" vanish or improved in the
future versions?