diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index cb469255d0a..395ddb40574 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -872,16 +872,11 @@ namespace ts {
     /** Does nothing. */
     export function noop(): void {}
 
-    /** A function not intended to be implemented. */
+    /** Throws an error because a function is not implemented. */
     export function notImplemented(): never {
         throw new Error("Not implemented");
     }
 
-    /** A function which isn't implemented, but should be eventually. */
-    export function notYetImplemented(): never {
-        throw new Error("TODO: Not yet implemented");
-    }
-
     export function memoize<T>(callback: () => T): () => T {
         let value: T;
         return () => {
diff --git a/src/harness/harness.ts b/src/harness/harness.ts
index 32681421d24..409ab9e2fcc 100644
--- a/src/harness/harness.ts
+++ b/src/harness/harness.ts
@@ -1668,7 +1668,7 @@ namespace Harness {
         // This does not need to exist strictly speaking, but many tests will need to be updated if it's removed
         export function compileString(_code: string, _unitName: string, _callback: (result: CompilerResult) => void) {
             // NEWTODO: Re-implement 'compileString'
-            return ts.notYetImplemented();
+            return ts.notImplemented();
         }
 
         export interface GeneratedFile {
diff --git a/src/harness/harnessLanguageService.ts b/src/harness/harnessLanguageService.ts
index a2e1f52f7ea..889d4f28ce9 100644
--- a/src/harness/harnessLanguageService.ts
+++ b/src/harness/harnessLanguageService.ts
@@ -313,7 +313,7 @@ namespace Harness.LanguageService {
         getLocalizedDiagnosticMessages(): string { return JSON.stringify({}); }
 
         readDirectory(_rootDir: string, _extension: string): string {
-            return ts.notYetImplemented();
+            return ts.notImplemented();
         }
         readDirectoryNames = ts.notImplemented;
         readFileNames = ts.notImplemented;
@@ -335,7 +335,7 @@ namespace Harness.LanguageService {
         constructor(private shim: ts.ClassifierShim) {
         }
         getEncodedLexicalClassifications(_text: string, _lexState: ts.EndOfLineState, _classifyKeywordsInGenerics?: boolean): ts.Classifications {
-            return ts.notYetImplemented();
+            return ts.notImplemented();
         }
         getClassificationsForLine(text: string, lexState: ts.EndOfLineState, classifyKeywordsInGenerics?: boolean): ts.ClassificationResult {
             const result = this.shim.getClassificationsForLine(text, lexState, classifyKeywordsInGenerics).split("\n");
@@ -644,7 +644,7 @@ namespace Harness.LanguageService {
         }
 
         createDirectory(_directoryName: string): void {
-            return ts.notYetImplemented();
+            return ts.notImplemented();
         }
 
         getCurrentDirectory(): string {
@@ -660,7 +660,7 @@ namespace Harness.LanguageService {
         }
 
         readDirectory(_path: string, _extension?: string[], _exclude?: string[], _include?: string[]): string[] {
-            return ts.notYetImplemented();
+            return ts.notImplemented();
         }
 
         watchFile(): ts.FileWatcher {
diff --git a/src/harness/unittests/cachingInServerLSHost.ts b/src/harness/unittests/cachingInServerLSHost.ts
index f930ab393d3..953edd98b6a 100644
--- a/src/harness/unittests/cachingInServerLSHost.ts
+++ b/src/harness/unittests/cachingInServerLSHost.ts
@@ -26,10 +26,10 @@ namespace ts {
                 return path in fileMap ? fileMap[path].content : undefined;
             },
             writeFile: (_path: string, _data: string, _writeByteOrderMark?: boolean) => {
-                return ts.notYetImplemented();
+                return ts.notImplemented();
             },
             resolvePath: (_path: string): string => {
-                return ts.notYetImplemented();
+                return ts.notImplemented();
             },
             fileExists: (path: string): boolean => {
                 return path in fileMap;
@@ -47,7 +47,7 @@ namespace ts {
             getDirectories: () => [],
             getEnvironmentVariable: () => "",
             readDirectory: (_path: string, _extension?: string[], _exclude?: string[], _include?: string[]): string[] => {
-                return ts.notYetImplemented();
+                return ts.notImplemented();
             },
             exit: noop,
             watchFile: () => ({
diff --git a/src/harness/unittests/reuseProgramStructure.ts b/src/harness/unittests/reuseProgramStructure.ts
index 29bb9a05b7c..0d3a8b3977a 100644
--- a/src/harness/unittests/reuseProgramStructure.ts
+++ b/src/harness/unittests/reuseProgramStructure.ts
@@ -111,7 +111,7 @@ namespace ts {
             getDefaultLibFileName(): string {
                 return "lib.d.ts";
             },
-            writeFile: notYetImplemented,
+            writeFile: notImplemented,
             getCurrentDirectory(): string {
                 return "";
             },
diff --git a/src/harness/unittests/tsserverProjectSystem.ts b/src/harness/unittests/tsserverProjectSystem.ts
index ff92f556eab..2abfd66b983 100644
--- a/src/harness/unittests/tsserverProjectSystem.ts
+++ b/src/harness/unittests/tsserverProjectSystem.ts
@@ -521,8 +521,8 @@ namespace ts.projectSystem {
         readonly resolvePath = (s: string) => s;
         readonly getExecutingFilePath = () => this.executingFilePath;
         readonly getCurrentDirectory = () => this.currentDirectory;
-        readonly exit = notYetImplemented;
-        readonly getEnvironmentVariable = notYetImplemented;
+        readonly exit = notImplemented;
+        readonly getEnvironmentVariable = notImplemented;
     }
 
     export function makeSessionRequest<T>(command: string, args: T) {
diff --git a/src/server/client.ts b/src/server/client.ts
index baa47ac6381..3b09a926754 100644
--- a/src/server/client.ts
+++ b/src/server/client.ts
@@ -242,7 +242,7 @@ namespace ts.server {
         }
 
         getCompletionEntrySymbol(_fileName: string, _position: number, _entryName: string): Symbol {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getNavigateToItems(searchValue: string): NavigateToItem[] {
@@ -415,7 +415,7 @@ namespace ts.server {
         }
 
         getEmitOutput(_fileName: string): EmitOutput {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getSyntacticDiagnostics(fileName: string): Diagnostic[] {
@@ -457,7 +457,7 @@ namespace ts.server {
         }
 
         getCompilerOptionsDiagnostics(): Diagnostic[] {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getRenameInfo(fileName: string, position: number, findInStrings?: boolean, findInComments?: boolean): RenameInfo {
@@ -562,11 +562,11 @@ namespace ts.server {
         }
 
         getNameOrDottedNameSpan(_fileName: string, _startPos: number, _endPos: number): TextSpan {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getBreakpointStatementAtPosition(_fileName: string, _position: number): TextSpan {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getSignatureHelpItems(fileName: string, position: number): SignatureHelpItems {
@@ -656,19 +656,19 @@ namespace ts.server {
         }
 
         getOutliningSpans(_fileName: string): OutliningSpan[] {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getTodoComments(_fileName: string, _descriptors: TodoCommentDescriptor[]): TodoComment[] {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getDocCommentTemplateAtPosition(_fileName: string, _position: number): TextInsertion {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         isValidBraceCompletionAtPosition(_fileName: string, _position: number, _openingBrace: number): boolean {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getCodeFixesAtPosition(fileName: string, start: number, end: number, errorCodes: number[]): CodeAction[] {
@@ -735,23 +735,23 @@ namespace ts.server {
         }
 
         getIndentationAtPosition(_fileName: string, _position: number, _options: EditorOptions): number {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getSyntacticClassifications(_fileName: string, _span: TextSpan): ClassifiedSpan[] {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getSemanticClassifications(_fileName: string, _span: TextSpan): ClassifiedSpan[] {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getEncodedSyntacticClassifications(_fileName: string, _span: TextSpan): Classifications {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getEncodedSemanticClassifications(_fileName: string, _span: TextSpan): Classifications {
-            return notYetImplemented();
+            return notImplemented();
         }
 
         getProgram(): Program {