Simplify Nexter interface

This change allows a Nexter to be used in the same manner as a scanner
using a for graph.Next(it) {} construction.

It is important that graph.Next(it) and any associated it.Result() calls
operate on the same iterator.

graph/memstore/all_iterator.go

@@ -36,15 +36,13 @@ func (it *AllIterator) SubIterators() []graph.Iterator {
 	return nil
 }
 
-func (it *AllIterator) Next() (graph.Value, bool) {
-	next, out := it.Int64.Next()
-	if !out {
-		return next, out
+func (it *AllIterator) Next() bool {
+	if !it.Int64.Next() {
+		return false
 	}
-	i64 := next.(int64)
-	_, ok := it.ts.revIdMap[i64]
+	_, ok := it.ts.revIdMap[it.Int64.Result().(int64)]
 	if !ok {
 		return it.Next()
 	}
-	return next, out
+	return true
 }

graph/memstore/iterator.go

@@ -93,7 +93,7 @@ func (it *Iterator) Clone() graph.Iterator {
 
 func (it *Iterator) Close() {}
 
-func (it *Iterator) Next() (graph.Value, bool) {
+func (it *Iterator) Next() bool {
 	graph.NextLogIn(it)
 	if it.tree.Max() == nil || it.result == int64(it.tree.Max().(Int64)) {
 		return graph.NextLogOut(it, nil, false)

graph/memstore/triplestore.go

@@ -132,11 +132,8 @@ func (ts *TripleStore) tripleExists(t *quad.Quad) (bool, int64) {
 	}
 	it := NewLlrbIterator(smallest_tree, "")
 
-	for {
-		val, ok := it.Next()
-		if !ok {
-			break
-		}
+	for it.Next() {
+		val := it.Result()
 		if t.Equals(&ts.triples[val.(int64)]) {
 			return true, val.(int64)
 		}

graph/memstore/triplestore_iterator_optimize.go

@@ -37,10 +37,10 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := graph.Next(primary)
-			if !ok {
-				panic("Sizes lie")
+			if !graph.Next(primary) {
+				panic("unexpected size during optimize")
 			}
+			val := primary.Result()
 			newIt := ts.TripleIterator(it.Direction(), val)
 			nt := newIt.Tagger()
 			nt.CopyFrom(it)

graph/memstore/triplestore_test.go

@@ -114,10 +114,10 @@ func TestIteratorsAndNextResultOrderA(t *testing.T) {
 	outerAnd.AddSubIterator(fixed)
 	outerAnd.AddSubIterator(hasa)
 
-	val, ok := outerAnd.Next()
-	if !ok {
+	if !outerAnd.Next() {
 		t.Error("Expected one matching subtree")
 	}
+	val := outerAnd.Result()
 	if ts.NameOf(val) != "C" {
 		t.Errorf("Matching subtree should be %s, got %s", "barak", ts.NameOf(val))
 	}
@@ -138,8 +138,7 @@ func TestIteratorsAndNextResultOrderA(t *testing.T) {
 		t.Errorf("Unexpected result, got:%q expect:%q", got, expect)
 	}
 
-	val, ok = outerAnd.Next()
-	if ok {
+	if outerAnd.Next() {
 		t.Error("More than one possible top level output?")
 	}
 }
@@ -190,8 +189,7 @@ func TestRemoveTriple(t *testing.T) {
 	hasa := iterator.NewHasA(ts, innerAnd, quad.Object)
 
 	newIt, _ := hasa.Optimize()
-	_, ok := graph.Next(newIt)
-	if ok {
+	if graph.Next(newIt) {
 		t.Error("E should not have any followers.")
 	}
 }