mermaid/packages/parser

Mermaid Parser

Mermaid parser package

How the package works

The package exports a parse function that has two parameters:

declare function parse<T extends DiagramAST>(
  diagramType: keyof typeof initializers,
  text: string
): T;

How does a Langium-based parser work?

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.

• When to override Lexer?

  • To modify input before tokenizing.
  • To insert/modify tokens that cannot or have not been parsed.

• When to override LangiumParser?

  • To insert or modify attributes that can't be parsed.

• When to override ValueConverter?

  • To modify the returned value from the parser.