The EPO has a page on its website about "Computer-Implemented Inventions (CII)" where they answer the question "Why are such programs not patentable in Europe?". Unfortunately, the answer does not reflect the law, but the EPO interpretation of the law:
Why are such programs not patentable in Europe?
The EPO does not grant patents for computer programs or computer-implemented business methods that make no technical contribution. Programs for computers as such are excluded from patentability by virtue of Art. 52(2)(c) and (3) EPC. According to this patent law, a program for a computer is not patentable if it does not have the potential to cause a "further technical effect" which must go beyond the inherent technical interactions between hardware and software.
I think I will send an email to the EPO (you can contact Sabine Kruspig, she is an expert at the EPO and member of the Gesellschaft für Informatik) asking them to quote the part of the EPC where a "program for a computer is not patentable if it does not have the potential to cause a "further technical effect"".