README.md

Makeast

Makeast is a transpiler that helps you quickly generate abstract syntax tree classes and interfaces in JavaScript/TypeScript.

Why Use Makeast

• Quickly generate usable classes and interfaces.
• Fast prototype your idea when building parsers.
• Painless visitor pattern and factory class.

Example

Suppose you're going to build a arithmetic calculator. You can write the abstract syntax tree strucutre in a top-down manner.

@tag("kind", "SyntaxTreeKind")
tree SyntaxTreeNode {
  node Token {
    text: string
  }
  tree Expression {
    node BinaryExpression {
      operator: Token
      left: Expression
      right: Expression
    }
    node UnaryExpression {
      operator: Token
      operand: Expression
    }
    node NumericLiteral {
      raw: string
      parsed: number
    }
  }
}

Take a closer look of the description above.

• Keyword node indicates a syntax tree node in a leaf position. It will be translated into an interface.
• The keyword tree indicate a container for one or more nodes and trees. It will be transpiled into an union type of all sub nodes.
• The decorator @tag("kind", "SyntaxTreeKind") means generate an enum named SyntaxTreeNode together with the tree and every node inside the tree will be included as an enum constant.

Makeast will generate following TypeScript interfaces and enums for you.

export enum SyntaxTreeKind {
  Token,
  BinaryExpression,
  UnaryExpression,
  NumericLiteral,
}

export interface Token {
  kind: SyntaxTreeKind.Token;
  text: string;
}

export interface BinaryExpression {
  kind: SyntaxTreeKind.BinaryExpression;
  operator: Token;
  left: Expression;
  right: Expression;
}

export interface UnaryExpression {
  kind: SyntaxTreeKind.UnaryExpression;
  operator: Token;
  operand: Expression;
}

export interface NumericLiteral {
  kind: SyntaxTreeKind.NumericLiteral;
  raw: string;
  parsed: number;
}

type Expression = BinaryExpression | UnaryExpression | NumericLiteral;

type SyntaxTreeNode = Token | Expression;