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It may be because byte-code needs to be regenerated by the exact version of the environment that will be used by the user, it may be because proper installation requires to detect some features of the available development environment, it may be because an index file to the available modules needs to be updated, it may be because optional interfaces or their documentation are best installed into a directory that only exists and is known if X is already installed. There are a number of possible reasons. In general, you cannot expect the installation procedure of the development environment of language X to know about some obscure X-PPL interface. But the X-PPL can know about X and may have to in case we want to simplify the user's life. For example, we may decide to make the life of X-Prolog/PPL users simpler by installing under /usr/local/lib/X/X-<version>/... We can do so reliably only if X-Prolog version <version> is already installed. Remember that we often work with software/languages that are no more than research prototypes: we cannot expect they always do the right thing or provide the same functionalities/flexibility one can find in more professional software.
Ok, thanks - I got the point. Although I do not fully agree to the above, I do not know any better and thus I opt for a single package per language too. Still, I will take a careful look at debian/control to see, whether we could find a -- from my point of view -- better solution, at least for debian. There are solutions, such as /etc/alternatives , that might help in some cases.
Thank you for your patience, Michael