diff --git a/core/core.go b/core/core.go
index 7a3dd40..70f9cb7 100644
--- a/core/core.go
+++ b/core/core.go
@@ -60,4 +60,5 @@ func Init(dataPath string) error {
 	if Data.Pages == nil {
 		Data.Pages = make(map[url.URL]*Page)
 	}
+	return nil
 }
diff --git a/core/structs.go b/core/structs.go
index 28915e1..3162877 100644
--- a/core/structs.go
+++ b/core/structs.go
@@ -99,7 +99,7 @@ func (f *Feed) Len() int {
 
 // Less compares Published of Items[i], Items[k] and returns true if Items[i] is
 // before Items[j].
-func (f *Feed) Less(i, j int) {
+func (f *Feed) Less(i, j int) bool {
 	return f.Items[i].Published.Before(f.Items[j].Published)
 }
 
@@ -109,25 +109,25 @@ func (f *Feed) Swap(i, j int) {
 }
 
 // Lock locks both feed and page mutexes.
-func (j *JsonData) Lock() {
+func (j *FullData) Lock() {
 	j.FeedsMu.Lock()
 	j.PagesMu.Lock()
 }
 
 // Unlock unlocks both feed and page mutexes.
-func (j *JsonData) Unlock() {
+func (j *FullData) Unlock() {
 	j.FeedsMu.Unlock()
 	j.PagesMu.Unlock()
 }
 
 // RLock read-locks both feed and page mutexes.
-func (j *JsonData) RLock() {
+func (j *FullData) RLock() {
 	j.FeedsMu.RLock()
 	j.PagesMu.RLock()
 }
 
 // RUnlock read-unlocks both feed and page mutexes.
-func (j *JsonData) RUnlock() {
+func (j *FullData) RUnlock() {
 	j.FeedsMu.RUnlock()
 	j.PagesMu.RUnlock()
 }