what's the effect of test in ac_define_dir.m4

[Ionutz Borcoman]

Hi,

I'm new to autotools an need something like missing facility --*dir.

I've started playing with ac_define_dir.m4 from the autoconf archive:
http://www.gnu.org/software/ac-archive/Miscellaneous/ac_define_dir.html

My modified version looks to produce what I want, but I fail to 
understand how is it functioning. What's the purpose of those test lines 
? They're not in an if statement ! So what are they doing ?

TIA,

Ionutz