Function premiseAtom

engine/premise.go:25–55

(a ast.Atom, lookupFn func(p ast.Atom, cb func(ast.Atom) error) error, subst unionfind.UnionFind)

)

func premiseAtom(a ast.Atom, lookupFn func(p ast.Atom, cb func(ast.Atom) error) error, subst unionfind.UnionFind) ([]unionfind.UnionFind, error) {
	p, err := functional.EvalAtom(a, subst)
	if err != nil {
		return nil, err
	}
	var solutions []unionfind.UnionFind
	if p.Predicate.IsBuiltin() {
		ok, nsubsts, err := builtin.Decide(p, &subst)
		if err != nil {
			return nil, err
		}
		if !ok {
			return nil, nil // no solution
		}
		for _, nsubst := range nsubsts {
			solutions = append(solutions, *nsubst)
		}
		return solutions, nil
	}
	// Not a built-in predicate. Call lookupFn.
	lookupFn(p, func(fact ast.Atom) error {
		// TODO: This could be made a lot more efficient by using a persistent
		// data structure for composing the unionfind substitutions.
		if newSubst, err := unionfind.UnifyTermsExtend(p.Args, fact.Args, subst); err == nil {
			solutions = append(solutions, newSubst)
		}
		return nil
	})
	return solutions, nil

}

// premiseNegAtom semi-positive evaluation, i.e. looks up a and fails if it is present.
func premiseNegAtom(a ast.Atom, store factstore.ReadOnlyFactStore, subst unionfind.UnionFind) ([]unionfind.UnionFind, error) {