Switch Lexer to be a proper class, remove 'createLexer'

src/index.js

@@ -178,7 +178,7 @@ export {
   printLocation,
   printSourceLocation,
   // Lex
-  createLexer,
+  Lexer,
   TokenKind,
   // Parse
   parse,
@@ -207,7 +207,6 @@ export {
 } from './language';
 
 export type {
-  Lexer,
   ParseOptions,
   SourceLocation,
   Location,

src/language/__tests__/lexer-test.js

@@ -12,15 +12,15 @@ import { GraphQLError } from '../../error/GraphQLError';
 
 import { Source } from '../source';
 import { TokenKind } from '../tokenKind';
-import { createLexer, isPunctuatorTokenKind } from '../lexer';
+import { Lexer, isPunctuatorTokenKind } from '../lexer';
 
 function lexOne(str) {
-  const lexer = createLexer(new Source(str));
+  const lexer = new Lexer(new Source(str));
   return lexer.advance();
 }
 
 function lexSecond(str) {
-  const lexer = createLexer(new Source(str));
+  const lexer = new Lexer(new Source(str));
   lexer.advance();
   return lexer.advance();
 }
@@ -187,7 +187,7 @@ describe('Lexer', () => {
     try {
       const str = ['', '', '     ?', ''].join('\n');
       const source = new Source(str, 'foo.js', { line: 11, column: 12 });
-      createLexer(source).advance();
+      new Lexer(source).advance();
     } catch (error) {
       caughtError = error;
     }
@@ -206,7 +206,7 @@ describe('Lexer', () => {
     let caughtError;
     try {
       const source = new Source('?', 'foo.js', { line: 1, column: 5 });
-      createLexer(source).advance();
+      new Lexer(source).advance();
     } catch (error) {
       caughtError = error;
     }
@@ -847,7 +847,7 @@ describe('Lexer', () => {
 
   it('lex reports useful information for dashes in names', () => {
     const source = new Source('a-b');
-    const lexer = createLexer(source);
+    const lexer = new Lexer(source);
     const firstToken = lexer.advance();
     expect(firstToken).to.contain({
       kind: TokenKind.NAME,
@@ -872,7 +872,7 @@ describe('Lexer', () => {
       }
     `);
 
-    const lexer = createLexer(source);
+    const lexer = new Lexer(source);
     const startToken = lexer.token;
     let endToken;
     do {

src/language/index.js

@@ -13,8 +13,7 @@ export type { KindEnum } from './kinds';
 export { TokenKind } from './tokenKind';
 export type { TokenKindEnum } from './tokenKind';
 
-export { createLexer } from './lexer';
-export type { Lexer } from './lexer';
+export { Lexer } from './lexer';
 
 export { parse, parseValue, parseType } from './parser';
 export type { ParseOptions } from './parser';

src/language/lexer.js

@@ -10,83 +10,70 @@ import { dedentBlockStringValue } from './blockString';
 import { type TokenKindEnum, TokenKind } from './tokenKind';
 
 /**
- * Given a Source object, this returns a Lexer for that source.
+ * Given a Source object, creates a Lexer for that source.
  * A Lexer is a stateful stream generator in that every time
  * it is advanced, it returns the next token in the Source. Assuming the
  * source lexes, the final Token emitted by the lexer will be of kind
  * EOF, after which the lexer will repeatedly return the same EOF token
  * whenever called.
  */
-export function createLexer(source: Source): Lexer {
-  const startOfFileToken = new Tok(TokenKind.SOF, 0, 0, 0, 0, null);
-  const lexer: Lexer = {
-    source,
-    lastToken: startOfFileToken,
-    token: startOfFileToken,
-    line: 1,
-    lineStart: 0,
-    advance: advanceLexer,
-    lookahead,
-  };
-  return lexer;
-}
-
-function advanceLexer() {
-  this.lastToken = this.token;
-  const token = (this.token = this.lookahead());
-  return token;
-}
-
-function lookahead() {
-  let token = this.token;
-  if (token.kind !== TokenKind.EOF) {
-    do {
-      // Note: next is only mutable during parsing, so we cast to allow this.
-      token = token.next || ((token: any).next = readToken(this, token));
-    } while (token.kind === TokenKind.COMMENT);
-  }
-  return token;
-}
-
-/**
- * The return type of createLexer.
- */
-export type Lexer = {
-  source: Source,
+export class Lexer {
+  source: Source;
 
   /**
    * The previously focused non-ignored token.
    */
-  lastToken: Token,
+  lastToken: Token;
 
   /**
    * The currently focused non-ignored token.
    */
-  token: Token,
+  token: Token;
 
   /**
    * The (1-indexed) line containing the current token.
    */
-  line: number,
+  line: number;
 
   /**
    * The character offset at which the current line begins.
    */
-  lineStart: number,
+  lineStart: number;
+
+  constructor(source: Source) {
+    const startOfFileToken = new Tok(TokenKind.SOF, 0, 0, 0, 0, null);
+
+    this.source = source;
+    this.lastToken = startOfFileToken;
+    this.token = startOfFileToken;
+    this.line = 1;
+    this.lineStart = 0;
+  }
 
   /**
    * Advances the token stream to the next non-ignored token.
    */
-  advance(): Token,
+  advance(): Token {
+    this.lastToken = this.token;
+    const token = (this.token = this.lookahead());
+    return token;
+  }
 
   /**
    * Looks ahead and returns the next non-ignored token, but does not change
    * the Lexer's state.
    */
-  lookahead(): Token,
-
-  ...
-};
+  lookahead(): Token {
+    let token = this.token;
+    if (token.kind !== TokenKind.EOF) {
+      do {
+        // Note: next is only mutable during parsing, so we cast to allow this.
+        token = token.next || ((token: any).next = readToken(this, token));
+      } while (token.kind === TokenKind.COMMENT);
+    }
+    return token;
+  }
+}
 
 /**
  * @internal

src/language/parser.js

@@ -11,7 +11,7 @@ import { Kind } from './kinds';
 import { Source } from './source';
 import { DirectiveLocation } from './directiveLocation';
 import { type TokenKindEnum, TokenKind } from './tokenKind';
-import { type Lexer, createLexer, isPunctuatorTokenKind } from './lexer';
+import { Lexer, isPunctuatorTokenKind } from './lexer';
 import {
   type Location,
   type Token,
@@ -177,7 +177,7 @@ class Parser {
       `Must provide Source. Received: ${inspect(sourceObj)}`,
     );
 
-    this._lexer = createLexer(sourceObj);
+    this._lexer = new Lexer(sourceObj);
     this._options = options || {};
   }
 

src/utilities/__tests__/stripIgnoredCharacters-test.js

@@ -8,7 +8,7 @@ import invariant from '../../jsutils/invariant';
 
 import { parse } from '../../language/parser';
 import { Source } from '../../language/source';
-import { createLexer } from '../../language/lexer';
+import { Lexer } from '../../language/lexer';
 
 import { stripIgnoredCharacters } from '../stripIgnoredCharacters';
 
@@ -59,7 +59,7 @@ const nonPunctuatorTokens = [
 ];
 
 function lexValue(str) {
-  const lexer = createLexer(new Source(str));
+  const lexer = new Lexer(new Source(str));
   const value = lexer.advance().value;
 
   invariant(lexer.advance().kind === '<EOF>', 'Expected EOF');

src/utilities/stripIgnoredCharacters.js

@@ -4,7 +4,7 @@ import inspect from '../jsutils/inspect';
 
 import { Source } from '../language/source';
 import { TokenKind } from '../language/tokenKind';
-import { createLexer, isPunctuatorTokenKind } from '../language/lexer';
+import { Lexer, isPunctuatorTokenKind } from '../language/lexer';
 import {
   dedentBlockStringValue,
   getBlockStringIndentation,
@@ -71,7 +71,7 @@ export function stripIgnoredCharacters(source: string | Source): string {
   }
 
   const body = sourceObj.body;
-  const lexer = createLexer(sourceObj);
+  const lexer = new Lexer(sourceObj);
   let strippedBody = '';
 
   let wasLastAddedTokenNonPunctuator = false;

tstypes/index.d.ts

@@ -177,7 +177,7 @@ export {
   printLocation,
   printSourceLocation,
   // Lex
-  createLexer,
+  Lexer,
   TokenKind,
   // Parse
   parse,
@@ -206,7 +206,6 @@ export {
 } from './language';
 
 export {
-  Lexer,
   ParseOptions,
   SourceLocation,
   Location,

tstypes/language/index.d.ts

@@ -5,7 +5,7 @@ export { printLocation, printSourceLocation } from './printLocation';
 
 export { Kind, KindEnum } from './kinds';
 export { TokenKind, TokenKindEnum } from './tokenKind';
-export { createLexer, Lexer } from './lexer';
+export { Lexer } from './lexer';
 export { parse, parseValue, parseType, ParseOptions } from './parser';
 export { print } from './printer';
 export {

tstypes/language/lexer.d.ts

@@ -10,12 +10,7 @@ import { Source } from './source';
  * EOF, after which the lexer will repeatedly return the same EOF token
  * whenever called.
  */
-export function createLexer(source: Source): Lexer;
-
-/**
- * The return type of createLexer.
- */
-export interface Lexer {
+export class Lexer {
   source: Source;
 
   /**
@@ -38,6 +33,8 @@ export interface Lexer {
    */
   lineStart: number;
 
+  constructor(source: Source);
+
   /**
    * Advances the token stream to the next non-ignored token.
    */