[Exim] failed to expand condition...

Can somebody help me? The next condition fails to expand:

suffix = -*
condition = ${if eq
${perl{suffixcheck}{$local_part}{${substr_1:$local_part_suffix}}}{yes}
{yes}{no}}

suffixcheck is a simple perl script which return "yes" or "no".

What I am trying to accomplish is that if the perlscript returns yes, the
condition succeeds and if the scripts returns no, the conditions fails.

R.E. Brouwer
brouwer@???