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.

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