Method MergePredicate

ast/decl.go:319–357

MergePredicate returns the information from the merge predicate descriptor. A merge predicate is a three-place.

()

//
// A merge predicate is a three-place.
func (d Decl) MergePredicate() ([]int, PredicateSym) {
	bad := false
	var indices []int
	var mergePred PredicateSym
	d.findDescr(DescrMergePredicate, func(a Atom) {
		if len(a.Args) != 2 {
			bad = true
			return
		}
		var tgtVars []int
		if tgtListApply, ok := (a.Args)[0].(ApplyFn); ok && tgtListApply.Function.Symbol == "fn:list" {
			for _, tgtVar := range tgtListApply.Args {
				if tgtVar, ok := tgtVar.(Variable); ok {
					for j, declVar := range d.DeclaredAtom.Args {
						if declVar == tgtVar {
							tgtVars = append(tgtVars, j)
						}
					}
				}
			}
		}
		predNameConstant, ok := (a.Args)[1].(Constant)
		if !ok {
			bad = true
			return
		}
		predName, err := predNameConstant.StringValue()
		if err != nil {
			bad = true
			return
		}
		indices = tgtVars
		mergePred = PredicateSym{predName, 2*len(tgtVars) + 1}
	})
	if bad {
		return nil, PredicateSym{}
	}
	return indices, mergePred
}

// BoundDecl is a bound declaration for the arguments of a predicate.
//