> For the complete documentation index, see [llms.txt](https://radlohead.gitbook.io/typescript-deep-dive/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://radlohead.gitbook.io/typescript-deep-dive/overview/parser/parser-functions.md). # Parser Functions ## Parser Functions As mentioned `parseSourceFile` sets up the initial state and passes the work onto `parseSourceFileWorker` function. ### `parseSourceFileWorker` Starts by creating a `SourceFile` AST node. Then it goes into parsing source code starting from the `parseStatements` function. Once that returns, it then completes the `SourceFile` node with additional information such as its `nodeCount`, `identifierCount` and such. ### `parseStatements` One of the most significant `parseFoo` style functions (a concept we cover next). It switches by the current `token` returned from the scanner. E.g. if the current token is a `SemicolonToken` it will call out to `parseEmptyStatement` to create an AST node for an empty statement. ## Node creation The parser has a bunch of `parserFoo` functions with bodies that create `Foo` nodes. These are generally called (from other parser functions) at a time where a `Foo` node is expected. A typical sample of this process is the `parseEmptyStatement()` function which is used to parse out empty statements like `;;;;;;`. Here is the function in its entirety ```typescript function parseEmptyStatement(): Statement { let node = createNode(SyntaxKind.EmptyStatement); parseExpected(SyntaxKind.SemicolonToken); return finishNode(node); } ``` It shows three critical functions `createNode`, `parseExpected` and `finishNode`. ### `createNode` The parser's `createNode` function `function createNode(kind: SyntaxKind, pos?: number): Node` is responsible for creating a Node, setting up its `SyntaxKind` as passed in, and set the initial position if passed in (or use the position from the current scanner state). ### `parseExpected` The parser's `parseExpected` function `function parseExpected(kind: SyntaxKind, diagnosticMessage?: DiagnosticMessage): boolean` will check that the current token in the parser state matches the desired `SyntaxKind`. If not it will either report the `diagnosticMessage` sent in or create a generic one of the form `foo expected`. It internally uses the `parseErrorAtPosition` function (which uses the scanning positions) to give good error reporting. ## `finishNode` The parser's `finishNode` function `function finishNode(node: T, end?: number): T` sets up the `end` position for the node and additional useful stuff like the `parserContextFlags` it was parsed under as well as if there were any errors before parsing this node (if there were then we cannot reuse this AST node in incremental parsing). --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://radlohead.gitbook.io/typescript-deep-dive/overview/parser/parser-functions.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.