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/iterator.go

@@ -77,10 +77,14 @@ type Iterator interface {
 	// the iteration interface.
 	//
 	// To get the full results of iteration, do the following:
-	// while (!Next()):
-	//   emit result
-	//   while (!NextPath()):
-	//       emit result
+	//
+	//  for graph.Next(it) {
+	//  	val := it.Result()
+	//  	... do things with val.
+	//  	for it.NextPath() {
+	//  		... find other paths to iterate
+	//  	}
+	//  }
 	//
 	// All of them should set iterator.Last to be the last returned value, to
 	// make results work.
@@ -135,22 +139,22 @@ type Iterator interface {
 }
 
 type Nexter interface {
-	// Next() advances the iterator and returns the next valid result. Returns
-	// (<value>, true) or (nil, false)
-	Next() (Value, bool)
+	// Next advances the iterator to the next value, which will then be available through
+	// the Result method. It returns false if no further advancement is possible.
+	Next() bool
 
 	Iterator
 }
 
 // Next is a convenience function that conditionally calls the Next method
 // of an Iterator if it is a Nexter. If the Iterator is not a Nexter, Next
-// return a nil Value and false.
-func Next(it Iterator) (Value, bool) {
+// returns false.
+func Next(it Iterator) bool {
 	if n, ok := it.(Nexter); ok {
 		return n.Next()
 	}
 	glog.Errorln("Nexting an un-nextable iterator")
-	return nil, false
+	return false
 }
 
 // FixedIterator wraps iterators that are modifiable by addition of fixed value sets.
@@ -253,7 +257,7 @@ func NextLogIn(it Iterator) {
 	}
 }
 
-func NextLogOut(it Iterator, val Value, ok bool) (Value, bool) {
+func NextLogOut(it Iterator, val Value, ok bool) bool {
 	if glog.V(4) {
 		if ok {
 			glog.V(4).Infof("%s %d NEXT IS %d", strings.ToUpper(it.Type().String()), it.UID(), val)
@@ -261,5 +265,5 @@ func NextLogOut(it Iterator, val Value, ok bool) (Value, bool) {
 			glog.V(4).Infof("%s %d NEXT DONE", strings.ToUpper(it.Type().String()), it.UID())
 		}
 	}
-	return val, ok
+	return ok
 }

graph/iterator/all_iterator.go

@@ -87,7 +87,7 @@ func (it *Int64) DebugString(indent int) string {
 
 // Next() on an Int64 all iterator is a simple incrementing counter.
 // Return the next integer, and mark it as the result.
-func (it *Int64) Next() (graph.Value, bool) {
+func (it *Int64) Next() bool {
 	graph.NextLogIn(it)
 	if it.at == -1 {
 		return graph.NextLogOut(it, nil, false)

graph/iterator/and_iterator.go

@@ -151,25 +151,20 @@ func (it *And) AddSubIterator(sub graph.Iterator) {
 	it.itCount++
 }
 
-// Returns the Next value from the And iterator. Because the And is the
-// intersection of its subiterators, it must choose one subiterator to produce a
-// candidate, and check this value against the subiterators. A productive choice
-// of primary iterator is therefore very important.
-func (it *And) Next() (graph.Value, bool) {
+// Returns advances the And iterator. Because the And is the intersection of its
+// subiterators, it must choose one subiterator to produce a candidate, and check
+// this value against the subiterators. A productive choice of primary iterator
+// is therefore very important.
+func (it *And) Next() bool {
 	graph.NextLogIn(it)
-	var curr graph.Value
-	var exists bool
-	for {
-		curr, exists = graph.Next(it.primaryIt)
-		if !exists {
-			return graph.NextLogOut(it, nil, false)
-		}
+	for graph.Next(it.primaryIt) {
+		curr := it.primaryIt.Result()
 		if it.subItsContain(curr) {
 			it.result = curr
 			return graph.NextLogOut(it, curr, true)
 		}
 	}
-	panic("unreachable")
+	return graph.NextLogOut(it, nil, false)
 }
 
 func (it *And) Result() graph.Value {

graph/iterator/and_iterator_test.go

@@ -36,10 +36,10 @@ func TestTag(t *testing.T) {
 		t.Errorf("Cannot get tag back, got %s", out[0])
 	}
 
-	val, ok := and.Next()
-	if !ok {
+	if !and.Next() {
 		t.Errorf("And did not next")
 	}
+	val := and.Result()
 	if val != 234 {
 		t.Errorf("Unexpected value")
 	}
@@ -76,18 +76,15 @@ func TestAndAndFixedIterators(t *testing.T) {
 		t.Error("not accurate")
 	}
 
-	val, ok := and.Next()
-	if val != 3 || ok == false {
+	if !and.Next() || and.Result() != 3 {
 		t.Error("Incorrect first value")
 	}
 
-	val, ok = and.Next()
-	if val != 4 || ok == false {
+	if !and.Next() || and.Result() != 4 {
 		t.Error("Incorrect second value")
 	}
 
-	val, ok = and.Next()
-	if ok {
+	if and.Next() {
 		t.Error("Too many values")
 	}
 
@@ -117,8 +114,7 @@ func TestNonOverlappingFixedIterators(t *testing.T) {
 		t.Error("not accurate")
 	}
 
-	_, ok := and.Next()
-	if ok {
+	if and.Next() {
 		t.Error("Too many values")
 	}
 
@@ -131,18 +127,15 @@ func TestAllIterators(t *testing.T) {
 	and.AddSubIterator(all2)
 	and.AddSubIterator(all1)
 
-	val, ok := and.Next()
-	if val.(int64) != 4 || ok == false {
+	if !and.Next() || and.Result() != int64(4) {
 		t.Error("Incorrect first value")
 	}
 
-	val, ok = and.Next()
-	if val.(int64) != 5 || ok == false {
+	if !and.Next() || and.Result() != int64(5) {
 		t.Error("Incorrect second value")
 	}
 
-	val, ok = and.Next()
-	if ok {
+	if and.Next() {
 		t.Error("Too many values")
 	}
 

graph/iterator/fixed_iterator.go

@@ -135,8 +135,8 @@ func (it *Fixed) Contains(v graph.Value) bool {
 	return graph.ContainsLogOut(it, v, false)
 }
 
-// Return the next stored value from the iterator.
-func (it *Fixed) Next() (graph.Value, bool) {
+// Next advances the iterator.
+func (it *Fixed) Next() bool {
 	graph.NextLogIn(it)
 	if it.lastIndex == len(it.values) {
 		return graph.NextLogOut(it, nil, false)

graph/iterator/hasa_iterator.go

@@ -158,16 +158,13 @@ func (it *HasA) Contains(val graph.Value) bool {
 // result iterator (a triple iterator based on the last checked value) and returns true if
 // another match is made.
 func (it *HasA) NextContains() bool {
-	for {
-		linkVal, ok := graph.Next(it.resultIt)
-		if !ok {
-			break
-		}
+	for graph.Next(it.resultIt) {
+		link := it.resultIt.Result()
 		if glog.V(4) {
-			glog.V(4).Infoln("Quad is", it.ts.Quad(linkVal))
+			glog.V(4).Infoln("Quad is", it.ts.Quad(link))
 		}
-		if it.primaryIt.Contains(linkVal) {
-			it.result = it.ts.TripleDirection(linkVal, it.dir)
+		if it.primaryIt.Contains(link) {
+			it.result = it.ts.TripleDirection(link, it.dir)
 			return true
 		}
 	}
@@ -188,20 +185,20 @@ func (it *HasA) NextPath() bool {
 	return it.NextContains()
 }
 
-// Get the next result from this iterator. This is simpler than Contains. We have a
+// Next advances the iterator. This is simpler than Contains. We have a
 // subiterator we can get a value from, and we can take that resultant triple,
 // pull our direction out of it, and return that.
-func (it *HasA) Next() (graph.Value, bool) {
+func (it *HasA) Next() bool {
 	graph.NextLogIn(it)
 	if it.resultIt != nil {
 		it.resultIt.Close()
 	}
 	it.resultIt = &Null{}
 
-	tID, ok := graph.Next(it.primaryIt)
-	if !ok {
+	if !graph.Next(it.primaryIt) {
 		return graph.NextLogOut(it, 0, false)
 	}
+	tID := it.primaryIt.Result()
 	name := it.ts.Quad(tID).Get(it.dir)
 	val := it.ts.ValueOf(name)
 	it.result = val

graph/iterator/iterator.go

@@ -79,8 +79,8 @@ func (it *Null) DebugString(indent int) string {
 	return strings.Repeat(" ", indent) + "(null)"
 }
 
-func (it *Null) Next() (graph.Value, bool) {
-	return nil, false
+func (it *Null) Next() bool {
+	return false
 }
 
 func (it *Null) Result() graph.Value {

graph/iterator/linksto_iterator.go

@@ -153,23 +153,23 @@ func (it *LinksTo) Optimize() (graph.Iterator, bool) {
 }
 
 // Next()ing a LinksTo operates as described above.
-func (it *LinksTo) Next() (graph.Value, bool) {
+func (it *LinksTo) Next() bool {
 	graph.NextLogIn(it)
-	val, ok := graph.Next(it.nextIt)
-	if !ok {
-		// Subiterator is empty, get another one
-		candidate, ok := graph.Next(it.primaryIt)
-		if !ok {
-			// We're out of nodes in our subiterator, so we're done as well.
-			return graph.NextLogOut(it, 0, false)
-		}
-		it.nextIt.Close()
-		it.nextIt = it.ts.TripleIterator(it.dir, candidate)
-		// Recurse -- return the first in the next set.
-		return it.Next()
+	if graph.Next(it.nextIt) {
+		it.result = it.nextIt.Result()
+		return graph.NextLogOut(it, it.nextIt, true)
 	}
-	it.result = val
-	return graph.NextLogOut(it, val, ok)
+
+	// Subiterator is empty, get another one
+	if !graph.Next(it.primaryIt) {
+		// We're out of nodes in our subiterator, so we're done as well.
+		return graph.NextLogOut(it, 0, false)
+	}
+	it.nextIt.Close()
+	it.nextIt = it.ts.TripleIterator(it.dir, it.primaryIt.Result())
+
+	// Recurse -- return the first in the next set.
+	return it.Next()
 }
 
 func (it *LinksTo) Result() graph.Value {

graph/iterator/linksto_iterator_test.go

@@ -33,10 +33,10 @@ func TestLinksTo(t *testing.T) {
 	}
 	fixed.Add(val)
 	lto := NewLinksTo(ts, fixed, quad.Object)
-	val, ok := lto.Next()
-	if !ok {
+	if !lto.Next() {
 		t.Error("At least one triple matches the fixed object")
 	}
+	val = lto.Result()
 	if val != 2 {
 		t.Errorf("Quad index 2, such as %s, should match %s", ts.Quad(2), ts.Quad(val))
 	}

graph/iterator/optional_iterator.go

@@ -51,8 +51,6 @@ func NewOptional(it graph.Iterator) *Optional {
 	}
 }
 
-func (it *Optional) CanNext() bool { return false }
-
 func (it *Optional) UID() uint64 {
 	return it.uid
 }

graph/iterator/or_iterator.go

@@ -141,35 +141,34 @@ func (it *Or) AddSubIterator(sub graph.Iterator) {
 	it.itCount++
 }
 
-// Returns the Next value from the Or graph.iterator. Because the Or is the
-// union of its subiterators, it must produce from all subiterators -- unless
-// it's shortcircuiting, in which case, it's the first one that returns anything.
-func (it *Or) Next() (graph.Value, bool) {
+// Next advances the Or graph.iterator. Because the Or is the union of its
+// subiterators, it must produce from all subiterators -- unless it it
+// shortcircuiting, in which case, it is the first one that returns anything.
+func (it *Or) Next() bool {
 	graph.NextLogIn(it)
-	var curr graph.Value
-	var exists bool
-	firstTime := false
+	var first bool
 	for {
 		if it.currentIterator == -1 {
 			it.currentIterator = 0
-			firstTime = true
+			first = true
 		}
 		curIt := it.internalIterators[it.currentIterator]
-		curr, exists = graph.Next(curIt)
-		if !exists {
-			if it.isShortCircuiting && !firstTime {
-				return graph.NextLogOut(it, nil, false)
-			}
-			it.currentIterator++
-			if it.currentIterator == it.itCount {
-				return graph.NextLogOut(it, nil, false)
-			}
-		} else {
-			it.result = curr
-			return graph.NextLogOut(it, curr, true)
+
+		if graph.Next(curIt) {
+			it.result = curIt.Result()
+			return graph.NextLogOut(it, it.result, true)
+		}
+
+		if it.isShortCircuiting && !first {
+			break
+		}
+		it.currentIterator++
+		if it.currentIterator == it.itCount {
+			break
 		}
 	}
-	panic("unreachable")
+
+	return graph.NextLogOut(it, nil, false)
 }
 
 func (it *Or) Result() graph.Value {

graph/iterator/or_iterator_test.go

@@ -23,12 +23,8 @@ import (
 
 func iterated(it graph.Iterator) []int {
 	var res []int
-	for {
-		val, ok := graph.Next(it)
-		if !ok {
-			break
-		}
-		res = append(res, val.(int))
+	for graph.Next(it) {
+		res = append(res, it.Result().(int))
 	}
 	return res
 }

graph/iterator/query_shape.go

@@ -129,12 +129,8 @@ func (qs *queryShape) MakeNode(it graph.Iterator) *Node {
 		}
 	case graph.Fixed:
 		n.IsFixed = true
-		for {
-			val, more := graph.Next(it)
-			if !more {
-				break
-			}
-			n.Values = append(n.Values, qs.ts.NameOf(val))
+		for graph.Next(it) {
+			n.Values = append(n.Values, qs.ts.NameOf(it.Result()))
 		}
 	case graph.HasA:
 		hasa := it.(*HasA)

graph/iterator/value_comparison_iterator.go

@@ -127,20 +127,15 @@ func (it *Comparison) Clone() graph.Iterator {
 	return out
 }
 
-func (it *Comparison) Next() (graph.Value, bool) {
-	var val graph.Value
-	var ok bool
-	for {
-		val, ok = graph.Next(it.subIt)
-		if !ok {
-			return nil, false
-		}
+func (it *Comparison) Next() bool {
+	for graph.Next(it.subIt) {
+		val := it.subIt.Result()
 		if it.doComparison(val) {
-			break
+			it.result = val
+			return true
 		}
 	}
-	it.result = val
-	return val, ok
+	return false
 }
 
 // DEPRECATED

graph/iterator/value_comparison_iterator_test.go

@@ -69,12 +69,8 @@ func TestValueComparison(t *testing.T) {
 		vc := NewComparison(simpleFixedIterator(), test.operator, test.operand, ts)
 
 		var got []string
-		for {
-			val, ok := vc.Next()
-			if !ok {
-				break
-			}
-			got = append(got, ts.NameOf(val))
+		for vc.Next() {
+			got = append(got, ts.NameOf(vc.Result()))
 		}
 		if !reflect.DeepEqual(got, test.expect) {
 			t.Errorf("Failed to show %s, got:%q expect:%q", test.message, got, test.expect)

graph/leveldb/all_iterator.go

@@ -101,10 +101,10 @@ func (it *AllIterator) Clone() graph.Iterator {
 	return out
 }
 
-func (it *AllIterator) Next() (graph.Value, bool) {
+func (it *AllIterator) Next() bool {
 	if !it.open {
 		it.result = nil
-		return nil, false
+		return false
 	}
 	var out []byte
 	out = make([]byte, len(it.iter.Key()))
@@ -115,10 +115,10 @@ func (it *AllIterator) Next() (graph.Value, bool) {
 	}
 	if !bytes.HasPrefix(out, it.prefix) {
 		it.Close()
-		return nil, false
+		return false
 	}
 	it.result = out
-	return out, true
+	return true
 }
 
 func (it *AllIterator) ResultTree() *graph.ResultTree {

graph/leveldb/iterator.go

@@ -117,19 +117,19 @@ func (it *Iterator) Close() {
 	}
 }
 
-func (it *Iterator) Next() (graph.Value, bool) {
+func (it *Iterator) Next() bool {
 	if it.iter == nil {
 		it.result = nil
-		return nil, false
+		return false
 	}
 	if !it.open {
 		it.result = nil
-		return nil, false
+		return false
 	}
 	if !it.iter.Valid() {
 		it.result = nil
 		it.Close()
-		return nil, false
+		return false
 	}
 	if bytes.HasPrefix(it.iter.Key(), it.nextPrefix) {
 		out := make([]byte, len(it.iter.Key()))
@@ -139,11 +139,11 @@ func (it *Iterator) Next() (graph.Value, bool) {
 		if !ok {
 			it.Close()
 		}
-		return out, true
+		return true
 	}
 	it.Close()
 	it.result = nil
-	return nil, false
+	return false
 }
 
 func (it *Iterator) ResultTree() *graph.ResultTree {

graph/leveldb/leveldb_test.go

@@ -45,12 +45,8 @@ func makeTripleSet() []*quad.Quad {
 
 func iteratedTriples(qs graph.TripleStore, it graph.Iterator) []*quad.Quad {
 	var res ordered
-	for {
-		val, ok := graph.Next(it)
-		if !ok {
-			break
-		}
-		res = append(res, qs.Quad(val))
+	for graph.Next(it) {
+		res = append(res, qs.Quad(it.Result()))
 	}
 	sort.Sort(res)
 	return res
@@ -85,12 +81,8 @@ func (o ordered) Swap(i, j int) { o[i], o[j] = o[j], o[i] }
 
 func iteratedNames(qs graph.TripleStore, it graph.Iterator) []string {
 	var res []string
-	for {
-		val, ok := graph.Next(it)
-		if !ok {
-			break
-		}
-		res = append(res, qs.NameOf(val))
+	for graph.Next(it) {
+		res = append(res, qs.NameOf(it.Result()))
 	}
 	sort.Strings(res)
 	return res
@@ -266,8 +258,8 @@ func TestIterator(t *testing.T) {
 	it.Reset()
 
 	it = qs.TriplesAllIterator()
-	edge, _ := graph.Next(it)
-	triple := qs.Quad(edge)
+	graph.Next(it)
+	triple := qs.Quad(it.Result())
 	set := makeTripleSet()
 	var ok bool
 	for _, t := range set {

graph/leveldb/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/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.")
 	}
 }

graph/mongo/iterator.go

@@ -138,7 +138,7 @@ func (it *Iterator) Clone() graph.Iterator {
 	return m
 }
 
-func (it *Iterator) Next() (graph.Value, bool) {
+func (it *Iterator) Next() bool {
 	var result struct {
 		Id string "_id"
 		//Sub string "Sub"
@@ -151,10 +151,10 @@ func (it *Iterator) Next() (graph.Value, bool) {
 		if err != nil {
 			glog.Errorln("Error Nexting Iterator: ", err)
 		}
-		return nil, false
+		return false
 	}
 	it.result = result.Id
-	return result.Id, true
+	return true
 }
 
 func (it *Iterator) ResultTree() *graph.ResultTree {

graph/mongo/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/result_tree_evaluator.go

@@ -14,7 +14,10 @@
 
 package graph
 
-import "fmt"
+import (
+	"bytes"
+	"fmt"
+)
 
 type ResultTree struct {
 	result   Value
@@ -26,14 +29,13 @@ func NewResultTree(result Value) *ResultTree {
 }
 
 func (t *ResultTree) String() string {
-	base := fmt.Sprintf("(%d", t.result)
-	if len(t.subtrees) != 0 {
-		for _, sub := range t.subtrees {
-			base += fmt.Sprintf(" %s", sub)
-		}
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "(%d", t.result)
+	for _, sub := range t.subtrees {
+		fmt.Fprintf(&buf, " %s", sub)
 	}
-	base += ")"
-	return base
+	buf.WriteByte(')')
+	return buf.String()
 }
 
 func (t *ResultTree) AddSubtree(sub *ResultTree) {
@@ -41,22 +43,15 @@ func (t *ResultTree) AddSubtree(sub *ResultTree) {
 }
 
 func StringResultTreeEvaluator(it Nexter) string {
-	ok := true
-	out := ""
-	for {
-		_, ok = it.Next()
-		if !ok {
-			break
-		}
-		out += it.ResultTree().String()
-		out += "\n"
-		for it.NextPath() == true {
-			out += " "
-			out += it.ResultTree().String()
-			out += "\n"
+	var buf bytes.Buffer
+	for it.Next() {
+		fmt.Fprintln(&buf, it.ResultTree())
+		for it.NextPath() {
+			buf.WriteByte(' ')
+			fmt.Fprintln(&buf, it.ResultTree())
 		}
 	}
-	return out
+	return buf.String()
 }
 
 func PrintResultTreeEvaluator(it Nexter) {

query/gremlin/finals.go

@@ -151,8 +151,7 @@ func runIteratorToArray(it graph.Iterator, ses *Session, limit int) []map[string
 		if ses.doHalt {
 			return nil
 		}
-		_, ok := graph.Next(it)
-		if !ok {
+		if !graph.Next(it) {
 			break
 		}
 		tags := make(map[string]graph.Value)
@@ -187,11 +186,10 @@ func runIteratorToArrayNoTags(it graph.Iterator, ses *Session, limit int) []stri
 		if ses.doHalt {
 			return nil
 		}
-		val, ok := graph.Next(it)
-		if !ok {
+		if !graph.Next(it) {
 			break
 		}
-		output = append(output, ses.ts.NameOf(val))
+		output = append(output, ses.ts.NameOf(it.Result()))
 		count++
 		if limit >= 0 && count >= limit {
 			break
@@ -208,8 +206,7 @@ func runIteratorWithCallback(it graph.Iterator, ses *Session, callback otto.Valu
 		if ses.doHalt {
 			return
 		}
-		_, ok := graph.Next(it)
-		if !ok {
+		if !graph.Next(it) {
 			break
 		}
 		tags := make(map[string]graph.Value)
@@ -249,8 +246,7 @@ func runIteratorOnSession(it graph.Iterator, ses *Session) {
 		if ses.doHalt {
 			return
 		}
-		_, ok := graph.Next(it)
-		if !ok {
+		if !graph.Next(it) {
 			break
 		}
 		tags := make(map[string]graph.Value)

query/mql/session.go

@@ -88,11 +88,7 @@ func (s *Session) ExecInput(input string, c chan interface{}, limit int) {
 	if glog.V(2) {
 		glog.V(2).Infoln(it.DebugString(0))
 	}
-	for {
-		_, ok := graph.Next(it)
-		if !ok {
-			break
-		}
+	for graph.Next(it) {
 		tags := make(map[string]graph.Value)
 		it.TagResults(tags)
 		c <- tags

query/sexp/parser_test.go

@@ -67,10 +67,10 @@ func TestMemstoreBackedSexp(t *testing.T) {
 		if it.Type() != test.typ {
 			t.Errorf("Incorrect type for %s, got:%q expect %q", test.message, it.Type(), test.expect)
 		}
-		got, ok := graph.Next(it)
-		if !ok {
+		if !graph.Next(it) {
 			t.Errorf("Failed to %s", test.message)
 		}
+		got := it.Result()
 		if expect := ts.ValueOf(test.expect); got != expect {
 			t.Errorf("Incorrect result for %s, got:%v expect %v", test.message, got, expect)
 		}
@@ -88,10 +88,10 @@ func TestTreeConstraintParse(t *testing.T) {
 	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
-	out, ok := graph.Next(it)
-	if !ok {
+	if !graph.Next(it) {
 		t.Error("Got no results")
 	}
+	out := it.Result()
 	if out != ts.ValueOf("i") {
 		t.Errorf("Got %d, expected %d", out, ts.ValueOf("i"))
 	}
@@ -105,8 +105,7 @@ func TestTreeConstraintTagParse(t *testing.T) {
 		"(:like\n" +
 		"($a (:is :good))))"
 	it := BuildIteratorTreeForQuery(ts, query)
-	_, ok := graph.Next(it)
-	if !ok {
+	if !graph.Next(it) {
 		t.Error("Got no results")
 	}
 	tags := make(map[string]graph.Value)
@@ -135,15 +134,14 @@ func TestMultipleConstraintParse(t *testing.T) {
 	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
-	out, ok := graph.Next(it)
-	if !ok {
+	if !graph.Next(it) {
 		t.Error("Got no results")
 	}
+	out := it.Result()
 	if out != ts.ValueOf("i") {
 		t.Errorf("Got %d, expected %d", out, ts.ValueOf("i"))
 	}
-	_, ok = graph.Next(it)
-	if ok {
+	if graph.Next(it) {
 		t.Error("Too many results")
 	}
 }

query/sexp/session.go

@@ -77,11 +77,7 @@ func (s *Session) ExecInput(input string, out chan interface{}, limit int) {
 		fmt.Println(it.DebugString(0))
 	}
 	nResults := 0
-	for {
-		_, ok := graph.Next(it)
-		if !ok {
-			break
-		}
+	for graph.Next(it) {
 		tags := make(map[string]graph.Value)
 		it.TagResults(tags)
 		out <- &tags