[mathetic]

Ah, that's a problem with many facets.

It is not that we can't come up with a logic language that is more declarative, it is just that telling the program everything about the universe is so damn dull. For example, ordering of your body predicates will often be based on what you think intuitively their sizes of solutions are going to be e.g. `plus(A,B,C), solution(C,X).` You know that plus is injective, so you put it first but from a logical perspective putting solution predicate first is just as sensible. If the language allowed you to express relative sizes of the predicates, then this could have been done automatically, but it would involve coding the order of predicates somewhere else in the program!

You also need to get rid of cuts in Prolog, if you want to be closer to true declarative programming. You might like to then try Datalog (alas, not Turing complete).

Another approach is to separate concerns more clearly. The part of Prolog that encodes and solves a logical problem is often different than the one dealing with IO for example. Ideally, you want to be more declarative in the former domain and more imperative in the latter. This can (and probably have been done) with a monadic approach.

[iso-8859-1]

I made an online Datalog IDE with Lua extensions (Turing complete): http://ysangkok.github.io/mitre-datalog.js/wrapper.html

[Hendrikto]

I do not get why you mean by plus being injective.

`plus(1, 2, C). C = 3.`

`plus(0, 3, C). C = 3.`

Isn't that a counterexample, showing how it is not injective?

[mathetic]

Yes, I was thinking total with respect to _intuitive_ arguments, but wrote injective. Sorry.