diff --git a/Source/Modules/UIModules/CandidateUI/ctlCandidate.swift b/Source/Modules/UIModules/CandidateUI/ctlCandidate.swift
index 8d859201..7a79b603 100644
--- a/Source/Modules/UIModules/CandidateUI/ctlCandidate.swift
+++ b/Source/Modules/UIModules/CandidateUI/ctlCandidate.swift
@@ -116,19 +116,19 @@ public class ctlCandidate: NSWindowController, ctlCandidateProtocol {
 
   public func reloadData() {}
 
-  public func showNextPage() -> Bool {
+  @discardableResult public func showNextPage() -> Bool {
     false
   }
 
-  public func showPreviousPage() -> Bool {
+  @discardableResult public func showPreviousPage() -> Bool {
     false
   }
 
-  public func highlightNextCandidate() -> Bool {
+  @discardableResult public func highlightNextCandidate() -> Bool {
     false
   }
 
-  public func highlightPreviousCandidate() -> Bool {
+  @discardableResult public func highlightPreviousCandidate() -> Bool {
     false
   }
 
diff --git a/Source/Modules/UIModules/CandidateUI/ctlCandidateIMK.swift b/Source/Modules/UIModules/CandidateUI/ctlCandidateIMK.swift
index 6a71b98e..6db136a2 100644
--- a/Source/Modules/UIModules/CandidateUI/ctlCandidateIMK.swift
+++ b/Source/Modules/UIModules/CandidateUI/ctlCandidateIMK.swift
@@ -123,7 +123,7 @@ public class ctlCandidateIMK: IMKCandidates, ctlCandidateProtocol {
   }
 
   // 該函式會影響 IMK 選字窗。
-  public func showNextPage() -> Bool {
+  @discardableResult public func showNextPage() -> Bool {
     guard delegate != nil else { return false }
     if pageCount == 1 { return highlightNextCandidate() }
     if currentPageIndex + 1 >= pageCount { clsSFX.beep() }
@@ -135,7 +135,7 @@ public class ctlCandidateIMK: IMKCandidates, ctlCandidateProtocol {
   }
 
   // 該函式會影響 IMK 選字窗。
-  public func showPreviousPage() -> Bool {
+  @discardableResult public func showPreviousPage() -> Bool {
     guard delegate != nil else { return false }
     if pageCount == 1 { return highlightPreviousCandidate() }
     if currentPageIndex == 0 { clsSFX.beep() }
@@ -147,7 +147,7 @@ public class ctlCandidateIMK: IMKCandidates, ctlCandidateProtocol {
   }
 
   // 該函式會影響 IMK 選字窗。
-  public func highlightNextCandidate() -> Bool {
+  @discardableResult public func highlightNextCandidate() -> Bool {
     guard let delegate = delegate else { return false }
     selectedCandidateIndex =
       (selectedCandidateIndex + 1 >= delegate.candidateCountForController(self))
@@ -157,7 +157,7 @@ public class ctlCandidateIMK: IMKCandidates, ctlCandidateProtocol {
   }
 
   // 該函式會影響 IMK 選字窗。
-  public func highlightPreviousCandidate() -> Bool {
+  @discardableResult public func highlightPreviousCandidate() -> Bool {
     guard let delegate = delegate else { return false }
     selectedCandidateIndex =
       (selectedCandidateIndex == 0)
diff --git a/Source/Modules/UIModules/CandidateUI/ctlCandidateUniversal.swift b/Source/Modules/UIModules/CandidateUI/ctlCandidateUniversal.swift
index 60008b83..f291a656 100644
--- a/Source/Modules/UIModules/CandidateUI/ctlCandidateUniversal.swift
+++ b/Source/Modules/UIModules/CandidateUI/ctlCandidateUniversal.swift
@@ -432,7 +432,7 @@ public class ctlCandidateUniversal: ctlCandidate {
     layoutCandidateView()
   }
 
-  override public func showNextPage() -> Bool {
+  @discardableResult override public func showNextPage() -> Bool {
     guard delegate != nil else { return false }
     if pageCount == 1 { return highlightNextCandidate() }
     if currentPageIndex + 1 >= pageCount { clsSFX.beep() }
@@ -445,7 +445,7 @@ public class ctlCandidateUniversal: ctlCandidate {
     return true
   }
 
-  override public func showPreviousPage() -> Bool {
+  @discardableResult override public func showPreviousPage() -> Bool {
     guard delegate != nil else { return false }
     if pageCount == 1 { return highlightPreviousCandidate() }
     if currentPageIndex == 0 { clsSFX.beep() }
@@ -458,7 +458,7 @@ public class ctlCandidateUniversal: ctlCandidate {
     return true
   }
 
-  override public func highlightNextCandidate() -> Bool {
+  @discardableResult override public func highlightNextCandidate() -> Bool {
     guard let delegate = delegate else { return false }
     selectedCandidateIndex =
       (selectedCandidateIndex + 1 >= delegate.candidateCountForController(self))
@@ -466,7 +466,7 @@ public class ctlCandidateUniversal: ctlCandidate {
     return true
   }
 
-  override public func highlightPreviousCandidate() -> Bool {
+  @discardableResult override public func highlightPreviousCandidate() -> Bool {
     guard let delegate = delegate else { return false }
     selectedCandidateIndex =
       (selectedCandidateIndex == 0)