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By default this is\r\n // start=0 and end=tokens.length, unless an embeddedTokenSequence is specified.\r\n private _readerStartIndex: number;\r\n private _readerEndIndex: number;\r\n\r\n // The index of the next token to be read\r\n private _currentIndex: number;\r\n\r\n // The start of the range to be returned by extractAccumulatedSequence()\r\n private _accumulatedStartIndex: number;\r\n\r\n public constructor(parserContext: ParserContext, embeddedTokenSequence?: TokenSequence) {\r\n this._parserContext = parserContext;\r\n this.tokens = parserContext.tokens;\r\n\r\n if (embeddedTokenSequence) {\r\n if (embeddedTokenSequence.parserContext !== this._parserContext) {\r\n throw new Error('The embeddedTokenSequence must use the same parser context');\r\n }\r\n this._readerStartIndex = embeddedTokenSequence.startIndex;\r\n this._readerEndIndex = embeddedTokenSequence.endIndex;\r\n } else {\r\n this._readerStartIndex = 0;\r\n this._readerEndIndex = this.tokens.length;\r\n }\r\n\r\n this._currentIndex = this._readerStartIndex;\r\n this._accumulatedStartIndex = this._readerStartIndex;\r\n }\r\n\r\n /**\r\n * Extracts and returns the TokenSequence that was accumulated so far by calls to readToken().\r\n * The next call to readToken() will start a new accumulated sequence.\r\n */\r\n public extractAccumulatedSequence(): TokenSequence {\r\n if (this._accumulatedStartIndex === this._currentIndex) {\r\n // If this happens, it indicates a parser bug:\r\n throw new Error(\r\n 'Parser assertion failed: The queue should not be empty when' +\r\n ' extractAccumulatedSequence() is called'\r\n );\r\n }\r\n\r\n const sequence: TokenSequence = new TokenSequence({\r\n parserContext: this._parserContext,\r\n startIndex: this._accumulatedStartIndex,\r\n endIndex: this._currentIndex\r\n });\r\n\r\n this._accumulatedStartIndex = this._currentIndex;\r\n\r\n return sequence;\r\n }\r\n\r\n /**\r\n * Returns true if the accumulated sequence has any tokens yet. This will be false\r\n * when the TokenReader starts, and it will be false immediately after a call\r\n * to extractAccumulatedSequence(). Otherwise, it will become true whenever readToken()\r\n * is called.\r\n */\r\n public isAccumulatedSequenceEmpty(): boolean {\r\n return this._accumulatedStartIndex === this._currentIndex;\r\n }\r\n\r\n /**\r\n * Like extractAccumulatedSequence(), but returns undefined if nothing has been\r\n * accumulated yet.\r\n */\r\n public tryExtractAccumulatedSequence(): TokenSequence | undefined {\r\n if (this.isAccumulatedSequenceEmpty()) {\r\n return undefined;\r\n }\r\n return this.extractAccumulatedSequence();\r\n }\r\n\r\n /**\r\n * Asserts that isAccumulatedSequenceEmpty() should return false. If not, an exception\r\n * is throw indicating a parser bug.\r\n */\r\n public assertAccumulatedSequenceIsEmpty(): void {\r\n if (!this.isAccumulatedSequenceEmpty()) {\r\n // If this happens, it indicates a parser bug:\r\n const sequence: TokenSequence = new TokenSequence({\r\n parserContext: this._parserContext,\r\n startIndex: this._accumulatedStartIndex,\r\n endIndex: this._currentIndex\r\n });\r\n const tokenStrings: string[] = sequence.tokens.map((x) => x.toString());\r\n throw new Error(\r\n 'Parser assertion failed: The queue should be empty, but it contains:\\n' +\r\n JSON.stringify(tokenStrings)\r\n );\r\n }\r\n }\r\n\r\n /**\r\n * Returns the next token that would be returned by _readToken(), without\r\n * consuming anything.\r\n */\r\n public peekToken(): Token {\r\n return this.tokens[this._currentIndex];\r\n }\r\n\r\n /**\r\n * Returns the TokenKind for the next token that would be returned by _readToken(), without\r\n * consuming anything.\r\n */\r\n public peekTokenKind(): TokenKind {\r\n if (this._currentIndex >= this._readerEndIndex) {\r\n return TokenKind.EndOfInput;\r\n }\r\n return this.tokens[this._currentIndex].kind;\r\n }\r\n\r\n /**\r\n * Like peekTokenKind(), but looks ahead two tokens.\r\n */\r\n public peekTokenAfterKind(): TokenKind {\r\n if (this._currentIndex + 1 >= this._readerEndIndex) {\r\n return TokenKind.EndOfInput;\r\n }\r\n return this.tokens[this._currentIndex + 1].kind;\r\n }\r\n\r\n /**\r\n * Like peekTokenKind(), but looks ahead three tokens.\r\n */\r\n public peekTokenAfterAfterKind(): TokenKind {\r\n if (this._currentIndex + 2 >= this._readerEndIndex) {\r\n return TokenKind.EndOfInput;\r\n }\r\n return this.tokens[this._currentIndex + 2].kind;\r\n }\r\n\r\n /**\r\n * Extract the next token from the input stream and return it.\r\n * The token will also be appended to the accumulated sequence, which can\r\n * later be accessed via extractAccumulatedSequence().\r\n */\r\n public readToken(): Token {\r\n if (this._currentIndex >= this._readerEndIndex) {\r\n // If this happens, it's a parser bug\r\n throw new Error('Cannot read past end of stream');\r\n }\r\n const token: Token = this.tokens[this._currentIndex];\r\n if (token.kind === TokenKind.EndOfInput) {\r\n // We don't allow reading the EndOfInput token, because we want _peekToken()\r\n // to be always guaranteed to return a valid result.\r\n\r\n // If this happens, it's a parser bug\r\n throw new Error('The EndOfInput token cannot be read');\r\n }\r\n this._currentIndex++;\r\n return token;\r\n }\r\n\r\n /**\r\n * Returns the kind of the token immediately before the current token.\r\n */\r\n public peekPreviousTokenKind(): TokenKind {\r\n if (this._currentIndex === 0) {\r\n return TokenKind.EndOfInput;\r\n }\r\n return this.tokens[this._currentIndex - 1].kind;\r\n }\r\n\r\n /**\r\n * Remembers the current position in the stream.\r\n */\r\n public createMarker(): number {\r\n return this._currentIndex;\r\n }\r\n\r\n /**\r\n * Rewinds the stream pointer to a previous position in the stream.\r\n */\r\n public backtrackToMarker(marker: number): void {\r\n if (marker > this._currentIndex) {\r\n // If this happens, it's a parser bug\r\n throw new Error('The marker has expired');\r\n }\r\n\r\n this._currentIndex = marker;\r\n if (marker < this._accumulatedStartIndex) {\r\n this._accumulatedStartIndex = marker;\r\n }\r\n }\r\n}\r\n"]} |