Feature: smart context query reorderer

[timoniq]

Consider a predicate flatten non trivial:

: ?flatten_nt(int[][]) -> int[].
?flatten_nt([]) -> [].
?flatten_nt([x]) -> x.
?flatten_nt(array) -> flattened {
    flattened = append<int>(x, y);
    y = flatten_nt(t);
    linked(x, t) = array;
}

Predicate will fail if we try to instantiate array from flattened:

?- flatten_nt(x) = [1,2,3]
* too broad error *

to change this behaviour queries should be reordered

?flatten_nt(array) -> flattened {
    linked(x, t) = array;
    y = flatten_nt(t);
    flattened = append<int>(x, y);
}

the idea is to do that automatically

qcontext may have order field (a vector with order calculated on scope entering)

[2, 1, 0]

[timoniq]

Reorderings for each case can be generated during predfinal generation. (Body linking for each arguments I/U permutation)

[timoniq]

there is a room for improvement in adding support for unify, unify all, quantor statements