Fix/issues

lexer.go

@@ -44,6 +44,7 @@ const (
 func (t TokenType) String() string {
 	types := []string{
 		"EOF",
+		"Undefined",
 		"TagStart",
 		"TagEnd",
 		"TagKey",

pgn.go

@@ -519,7 +519,7 @@ func (p *Parser) parseVariation() error {
 		// the last move before the variation start
 		variationParent = parentMove.parent
 		// Reset position to where the variation starts
-		if variationParent.parent != nil {
+		if variationParent.parent != nil && variationParent.parent.position != nil {
 			p.game.pos = variationParent.parent.position.copy()
 			if newPos := p.game.pos.Update(variationParent); newPos != nil {
 				p.game.pos = newPos

polyglot.go

@@ -194,12 +194,12 @@ func LoadFromSource(source BookSource) (*PolyglotBook, error) {
 
 	buf := make([]byte, 16)
 	for {
-		_, err := source.Read(buf)
-		if err == io.EOF {
+		_, readErr := source.Read(buf)
+		if readErr == io.EOF {
 			break
 		}
-		if err != nil {
-			return nil, err
+		if readErr != nil {
+			return nil, readErr
 		}
 
 		entry := PolyglotEntry{

polyglot_test.go

@@ -3,6 +3,7 @@ package chess
 import (
 	"bytes"
 	"encoding/binary"
+	"errors"
 	"io"
 	"os"
 	"path/filepath"
@@ -60,7 +61,7 @@ func TestBytesBookSource(t *testing.T) {
 	// Test EOF
 	source.index = 32
 	n, err = source.Read(buf)
-	if err != io.EOF {
+	if !errors.Is(err, io.EOF) {
 		t.Errorf("Read() error = %v, want EOF", err)
 	}
 }