| 6dd74de | | | 1 | <p align="center"> |
| 6dd74de | | | 2 | <img src="https://raw.githubusercontent.com/mermaid-js/mermaid/develop/docs/public/favicon.svg" height="150"> |
| 6dd74de | | | 3 | |
| 6dd74de | | | 4 | </p> |
| 6dd74de | | | 5 | <h1 align="center"> |
| 6dd74de | | | 6 | Mermaid Parser |
| 6dd74de | | | 7 | </h1> |
| 6dd74de | | | 8 | |
| 6dd74de | | | 9 | <p align="center"> |
| 6dd74de | | | 10 | Mermaid parser package |
| 6dd74de | | | 11 | <p> |
| 6dd74de | | | 12 | |
| 6dd74de | | | 13 | [](https://www.npmjs.com/package/@mermaid-js/parser) |
| 6dd74de | | | 14 | |
| 6dd74de | | | 15 | ## How the package works |
| 6dd74de | | | 16 | |
| 6dd74de | | | 17 | The package exports a `parse` function that has two parameters: |
| 6dd74de | | | 18 | |
| 6dd74de | | | 19 | ```ts |
| 6dd74de | | | 20 | declare function parse<T extends DiagramAST>( |
| 6dd74de | | | 21 | diagramType: keyof typeof initializers, |
| 6dd74de | | | 22 | text: string |
| 6dd74de | | | 23 | ): T; |
| 6dd74de | | | 24 | ``` |
| 6dd74de | | | 25 | |
| 6dd74de | | | 26 | ## How does a Langium-based parser work? |
| 6dd74de | | | 27 | |
| 6dd74de | | | 28 | ```mermaid |
| 6dd74de | | | 29 | sequenceDiagram |
| 6dd74de | | | 30 | actor Package |
| 6dd74de | | | 31 | participant Module |
| 6dd74de | | | 32 | participant TokenBuilder |
| 6dd74de | | | 33 | participant Lexer |
| 6dd74de | | | 34 | participant Parser |
| 6dd74de | | | 35 | participant ValueConverter |
| 6dd74de | | | 36 | |
| 6dd74de | | | 37 | |
| 6dd74de | | | 38 | Package ->> Module: Create services |
| 6dd74de | | | 39 | Module ->> TokenBuilder: Override or/and<br>reorder rules |
| 6dd74de | | | 40 | TokenBuilder ->> Lexer: Read the string and transform<br>it into a token stream |
| 6dd74de | | | 41 | Lexer ->> Parser: Parse token<br>stream into AST |
| 6dd74de | | | 42 | Parser ->> ValueConverter: Clean/modify tokenized<br>rules returned value |
| 6dd74de | | | 43 | ValueConverter -->> Package: Return AST |
| 6dd74de | | | 44 | ``` |
| 6dd74de | | | 45 | |
| 6dd74de | | | 46 | - When to override `TokenBuilder`? |
| 6dd74de | | | 47 | - To override keyword rules. |
| 6dd74de | | | 48 | - To override terminal rules that need a custom function. |
| 6dd74de | | | 49 | - To manually reorder the list of rules. |
| 6dd74de | | | 50 | |
| 6dd74de | | | 51 | - When to override `Lexer`? |
| 6dd74de | | | 52 | - To modify input before tokenizing. |
| 6dd74de | | | 53 | - To insert/modify tokens that cannot or have not been parsed. |
| 6dd74de | | | 54 | |
| 6dd74de | | | 55 | - When to override `LangiumParser`? |
| 6dd74de | | | 56 | - To insert or modify attributes that can't be parsed. |
| 6dd74de | | | 57 | |
| 6dd74de | | | 58 | - When to override `ValueConverter`? |
| 6dd74de | | | 59 | - To modify the returned value from the parser. |