[Exim] Macros, .include, and conditional configuration

Hello,

I am trying to make a single configuration file which behaves differently
depending on flags set in a master config file.

Essentially what I am trying to simulate is:

.include /etc/config           # contains "FOO=yes"  (or may not)

.ifdef FOO                     # or .if FOO=yes
  ...series of lines
.endif

I am trying to avoid using an external preprocessor. Symlinking the whole
config file to one of a set (or using the -C flag) is not really flexible
enough.

Does anyone know of a way to achieve what I want? My attempts so far are
documented below :-)

Thanks,

Brian.

------------------------------------------------------------------------
Attempt 1:

FOO=configure-foo
.include /usr/exim/FOO
# Nope: says 'failed to open included configuration file /usr/exim/FOO'

Attempt 2:

FOO=.include /usr/exim/configure-foo
FOO
# Nope: says 'main option "" unknown'

Attempt 3:

FOO=#
FOO .include /usr/exim/configure-foo

works as expected, but

FOO=
FOO .include /usr/exim/configure-foo

fails with 'main option "" unknown'

Incidentally, you can't define an empty macro on the command line, and
defining it as a space also fails:

  # exim -DFOO
  exim abandoned: unknown, malformed, or incomplete option -DFOO
  # exim -DFOO=""
  exim abandoned: unknown, malformed, or incomplete option -DFOO=
  # exim -DFOO=" "
  2002-08-08 12:18:36 Exim configuration error in line 2:
    main option "" unknown

Attempt 4:

FOO=#
BAR=#

FOO hostlist host_accept_relay =
FOO .. more config lines
FOO ..
BAR hostlist host_accept_relay = 1.2.3.0/24
BAR .. more config lines
BAR ..

This actually works, but the main part of the configuration then becomes
very messy with every line prefixed with FOO or BAR.

I also can't see a way of including a section if "FOO or BAR" is true,
or if "FOO and BAR" is true: e.g.

FOO=#
BAR=#
FOOBAR daemon_smtp_port=25

gives 'main option "" unknown'