I'm sure this is awesome, but there's no code examples until I download a read a PDF tutorial. I think a couple of examples in the README or on the homepage could go a long way. What differiates this from Prolog or Datalog?
Yeah, I definitely think this is something that could be improved - Mercury tends to come from a more 'old-school' form of OSS where the importance of marketing and design was less well understood. I hope they get around to fixing this!
The biggest thing that Mercury brings to the table is types, a mode system, and performance. This makes it viable for large scale software development.
There's still an interesting question about whether a different iteration on the mode system could capture more of the semantics of Prolog while still being useful, but so far nobody has done that research yet. It's more trendy to do FP research these days, so I'm expecting it could be a _long_ time before we get an answer, sadly.