Handle comments in N-Quad documents and REPL

The parser rejects an N-Quad with a comment, so we filter those out
ahead of time. This simplifies the grammar and code generated by the
parser.

db/repl.go

@@ -99,6 +99,11 @@ func Repl(ts graph.TripleStore, queryLanguage string, cfg *config.Config) error
 		if len(line) == 0 {
 			continue
 		}
+		line = bytes.TrimSpace(line)
+		if len(line) == 0 || line[0] == '#' {
+			line = line[:0]
+			continue
+		}
 		if bytes.HasPrefix(line, []byte(":debug")) {
 			ses.ToggleDebug()
 			fmt.Println("Debug Toggled")

nquads/nquads.go

@@ -16,6 +16,7 @@ package nquads
 
 import (
 	"bufio"
+	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -47,17 +48,24 @@ func NewDecoder(r io.Reader) *Decoder {
 
 func (dec *Decoder) Unmarshal() (*graph.Triple, error) {
 	dec.line = dec.line[:0]
+	var line []byte
 	for {
-		l, pre, err := dec.r.ReadLine()
-		if err != nil {
-			return nil, err
+		for {
+			l, pre, err := dec.r.ReadLine()
+			if err != nil {
+				return nil, err
+			}
+			dec.line = append(dec.line, l...)
+			if !pre {
+				break
+			}
 		}
-		dec.line = append(dec.line, l...)
-		if !pre {
+		if line = bytes.TrimSpace(dec.line); len(line) != 0 && line[0] != '#' {
 			break
 		}
+		dec.line = dec.line[:0]
 	}
-	triple, err := Parse(string(dec.line))
+	triple, err := Parse(string(line))
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse %q: %v", dec.line, err)
 	}

nquads/nquads_test.go

@@ -16,7 +16,9 @@ package nquads
 
 import (
 	"fmt"
+	"io"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/google/cayley/graph"
@@ -428,6 +430,56 @@ func TestParse(t *testing.T) {
 	}
 }
 
+// This is a sample taken from 30kmovies.nq.
+// It has intentional defects:
+// The second comment is inset one psace and
+// the second line after that comment is blank.
+var document = `# first 10 lines of 30kmovies.nq
+_:100000 </film/performance/actor> </en/larry_fine_1902> .
+_:100001 </film/performance/actor> </en/samuel_howard> .
+_:100002 </film/performance/actor> </en/joe_palma> .
+_:100003 </film/performance/actor> </en/symona_boniface> .
+_:100004 </film/performance/actor> </en/dudley_dickerson> .
+_:100005 </film/performance/actor> </guid/9202a8c04000641f8000000006ec181a> .
+_:100006 </film/performance/actor> </en/emil_sitka> .
+_:100007 </film/performance/actor> </en/christine_mcintyre> .
+_:100008 </film/performance/actor> </en/moe_howard> .
+_:100009 </film/performance/actor> </en/larry_fine_1902> .
+ #last ten lines of 30kmovies.nq
+</guid/9202a8c04000641f800000001473e673> <name> "Bill Fishman" .
+
+</guid/9202a8c04000641f800000001473e673> <type> </people/person> .
+</guid/9202a8c04000641f800000001474a221> <name> "Matthew J. Evans" .
+</guid/9202a8c04000641f800000001474a221> <type> </people/person> .
+</guid/9202a8c04000641f800000001474f486> <name> "Nina Bonherry" .
+</guid/9202a8c04000641f800000001474f486> <type> </people/person> .
+</user/basketball_loader/basketballdatabase_namespace/ROBERBI01> <name> "Bill Roberts" .
+</user/basketball_loader/basketballdatabase_namespace/ROBERBI01> <type> </people/person> .
+</user/jamie/nytdataid/N17971793050606542713> <name> "Christopher Ashley" .
+</user/jamie/nytdataid/N17971793050606542713> <type> </people/person> .
+`
+
+func TestDecoder(t *testing.T) {
+	dec := NewDecoder(strings.NewReader(document))
+	var n int
+	for {
+		triple, err := dec.Unmarshal()
+		if err != nil {
+			if err != io.EOF {
+				t.Fatalf("Failed to read document:", err)
+			}
+			break
+		}
+		if triple.Subject == "" || triple.Predicate == "" || triple.Object == "" {
+			t.Errorf("Unexpected triple, got:%v", triple)
+		}
+		n++
+	}
+	if n != 20 {
+		t.Errorf("Unexpected number of triples read, got:%d expect:20", n)
+	}
+}
+
 var result *graph.Triple
 
 func BenchmarkParser(b *testing.B) {