Introduction

Tools to parse a Curtis VCL source file into an AST. You can also pretty-print the AST back into a text file, or extend the provided parser to create extensions to the language.

Installation

npm install vcl-tools

# OR

yarn add vcl-tools

Usage

import { parseVCLtoAST, Program, BitDeclaration, Identifier } from 'vcl-tools'

const ast = parseVCLtoAST(new Program(
  [
    new VariableDeclaration(Identifier.from('incoming_data')),
    new BitDeclaration(Identifier.from('incoming_data_first_byte'), 
                       Identifier.from('incoming_data'), 15)
  ]))
new VCLAstPrinter().print(ast)

/** Output:
 * Create incoming_data variable
 * incoming_data_first_byte bit incoming_data.15
 */

High level API

parseVCLtoAST(vclContent: string)

A function that accepts a VCL source string and outputs an AST.

reprintVCL(vclContent: string)

A function that accepts a VCL source string and outputs a pretty-printed formatted source string.

VCLASTVisitor

A generic VCL visitor. Inherit and override specific methods to quickly go over a VCL AST. See example below.

Low level building blocks

parse(vclContent: string)

A function that accepts a VCL source string and outputs a CST, along with potential errors.

Useful for creating a basic compiler that doesn't require using VCL Studio.

Returns the following type:

{
  cst: cst,
  lexErrors: lexResult.errors,
  parseErrors: parser.errors,
};

VCLLexer

A chevrotain based lexer class

VCLParser

A chevrotain based parser class

VCLAstCreatorVisitor

A chevrotain based CST visitor

VCLAstPrinter

Pretty-print VCL AST.

example

import {
  VCLAstPrinter,
  WhileStatement, Literal, BlockStatement,
  AssignmentStatement, Identifier
} from 'vcl-tools'

new VCLAstPrinter().print(new WhileStatement(
  new Literal('1', 1),
  new BlockStatement([
    new AssignmentStatement(new Identifier('a'), new Literal('2', 2)),
    new AssignmentStatement(new Identifier('c'), new Literal('3', 3)),
  ])
))

/** Output:
 * while (1)
 * {
 *  a = 2
 *  c = 3
 * }
 */

AST types

Every type of VCL source code can be created programmatically using named imports from vcl-tools. This will allow you to generate any type of VCL code using VCLAstPrinter.

Statements

• Program
• ExpressionStatement
• BlockStatement
• AssignmentStatement
• LabelStatement
• CallStatement
• EnterStatement
• GoToStatement
• IfStatement
• WhileStatement
• ReturnStatement
• ExitStatement
• VariableDeclaration
• ConstantDeclaration
• AliasDeclaration
• EqualsDeclaration
• BitDeclaration
• IncludeStatement
• ModuleStatement

Expressions

• Identifier
• Literal
• CallExpression
• BinaryExpression
• UnaryExpression
• LogicalExpression

More examples:

Finding all CAN mailboxes using VCLASTVisitor

This example uses VCLASTVisitor to locate all CAN mailboxes used in a VCL source file, and fill a field mailboxes with the results (using a custom data structure CanMailbox).

import { VCLASTVisitor, Identifier, Literal } from 'vcl-tools'

enum BuiltInFunctions {
  SETUP_CAN_RECEIVE_MAILBOX = 'Setup_CAN_Receive_Mailbox',
  SETUP_CAN_TRANSMIT_MAILBOX = 'Setup_CAN_Transmit_Mailbox',
  SETUP_CAN_RECEIVE_DATA = 'Setup_CAN_Receive_Data',
  SETUP_CAN_TRANSMIT_DATA = 'Setup_CAN_Transmit_data',
}


export class MailboxExtractorVisitor extends VCLASTVisitor {
  mailboxes: Record<string, CanMailbox> = {};

  private getBuiltInFunction(identifier: string) {
    const match = Object.keys(BuiltInFunctions).find(
      (x) => x.toLowerCase() === identifier.toLowerCase()
    );
    if (match) {
      return (BuiltInFunctions as Record<string, BuiltInFunctions>)[match];
    }
    return null;
  };

  visitCallExpression(node: CallExpression) {
    super.visitCallExpression(node);
    const callee = node.callee.name;
    let functionName = this.getBuiltInFunction(callee);
    if (
      functionName === BuiltInFunctions.SETUP_CAN_RECEIVE_MAILBOX
    ) {
      const mailboxName = (node.arguments[0] as Identifier).toString();
      const mailboxId = (node.arguments[2] as Literal).value as number

      this.mailboxes[mailboxName] = new IncomingCanMailbox(
        mailboxId.toString(),
        mailboxName,
        []
      );
    } else if (
      functionName === BuiltInFunctions.SETUP_CAN_TRANSMIT_MAILBOX
    ) {
      const mailboxName = (node.arguments[0] as Identifier).toString();
      const mailboxId = (node.arguments[2] as Literal).value as number
      const type = node.arguments[4] as Identifier;
      const interval = node.arguments[5] as Literal;
      this.mailboxes[mailboxName] = new OutgoingCanMailbox(
        mailboxId.toString(),
        mailboxName,
        [],
        type.name === 'C_CYCLIC' ? 'cyclic' : 'event',
        interval?.value as number
      );
    } else if (
      functionName === BuiltInFunctions.SETUP_CAN_RECEIVE_DATA ||
      functionName === BuiltInFunctions.SETUP_CAN_TRANSMIT_DATA
    ) {
      const mailbox = (node.arguments[0] as Identifier).name;
      const field = (node.arguments[1] as Identifier).name;
      const bytes = (node.arguments[2] as Literal).value as number;
      const endianness =
        ((node.arguments[3] as Literal).value as number) === 0
          ? 'little'
          : 'big';
      this.mailboxes[mailbox].structure.push({ field, endianness, bytes });
    }
  }

Known errors:

1. The code formatter is very basic. A much better solution will be to re implement it as a prettier plugin (similar to this)