| <p align="center"> |
| <img src="https://raw.githubusercontent.com/mermaid-js/mermaid/develop/docs/public/favicon.svg" height="150"> |
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| </p> |
| <h1 align="center"> |
| Mermaid Parser |
| </h1> |
|
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| <p align="center"> |
| Mermaid parser package |
| <p> |
|
|
| [](https://www.npmjs.com/package/@mermaid-js/parser) |
|
|
| ## How the package works |
|
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| The package exports a `parse` function that has two parameters: |
|
|
| ```ts |
| declare function parse<T extends DiagramAST>( |
| diagramType: keyof typeof initializers, |
| text: string |
| ): T; |
| ``` |
|
|
| ## How does a Langium-based parser work? |
|
|
| ```mermaid |
| sequenceDiagram |
| actor Package |
| participant Module |
| participant TokenBuilder |
| participant Lexer |
| participant Parser |
| participant ValueConverter |
| |
| |
| Package ->> Module: Create services |
| Module ->> TokenBuilder: Override or/and<br>reorder rules |
| TokenBuilder ->> Lexer: Read the string and transform<br>it into a token stream |
| Lexer ->> Parser: Parse token<br>stream into AST |
| Parser ->> ValueConverter: Clean/modify tokenized<br>rules returned value |
| ValueConverter -->> Package: Return AST |
| ``` |
|
|
| - When to override `TokenBuilder`? |
| - To override keyword rules. |
| - To override terminal rules that need a custom function. |
| - To manually reorder the list of rules. |
|
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| - When to override `Lexer`? |
| - To modify input before tokenizing. |
| - To insert/modify tokens that cannot or have not been parsed. |
|
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| - When to override `LangiumParser`? |
| - To insert or modify attributes that can't be parsed. |
|
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| - When to override `ValueConverter`? |
| - To modify the returned value from the parser. |
|
|
