how to know path to BOOST_ROOT

From: Toon Knapen (toon.knapen_at_[hidden])
Date: 2004-09-03 05:32:33

In the mipspro toolset for bjamv2 (which I'm working on) I need to add 
the path $(BOOST_ROOT)/boost/compatibility/cpp_c_headers to the 
C++FLAGS. But for that I need to know BOOST_ROOT. I was hoping a 
variable BOOST_ROOT would be defined that points to this location but I 
tried

local boost_root = [ modules.peek : BOOST_ROOT ] ;
ECHO $(boost_root) ;

but it turns out to be empty (although another toolset uses the same 
trick). Any ideas about how i can do this ?