Path variables and path substitution

[John Ling]

Hello, I have some very long paths defined in my Makefile.am and I would 
like to clean things up by substituting them with a variable.  For 
example, if I have:

mylib_a_SOURCES = dir1/dir2/dir3/dir4/app.cpp
I want to define a variable, in Makefile.am, like so,
MYDIR = dir1/dir2/dir3/dir4
then I can change the SOURCES definition to be
mylib_a_SOURCES = $(MYDIR)/app.cpp
However, when I try this, everytime I run configure for some reason I 
get dependency errors saying it can't find the app.Po file in the .dep/ 
directory.  In addition, it creates a subdirectory that is literally 
called '$(MYDIR)' which is not what I intend to happen.

How do I do this path variable substitution?
Thanks,
John