pegjs-coffee-plugin/index.js

A plugin for PEG.js to use CoffeeScript in your actions.

//
// pegjs-coffee-plugin
//

var CoffeeScript = require('coffee-script')
var detectIndent = require('detect-indent')

// The acutal compilation of CoffeeScript.
function compileCoffeeScript (code) {
  // Compile options
  var options = {
    bare: true
  }

  try {
    return CoffeeScript.compile(code, options)
  } catch (error) {
    var message = 'In: \n' + code + '\n was the following error:' + error.message
    throw new SyntaxError(message, error.fileName, error.lineNumber)
  }
}

// The initializer gets its own scope which we save
// in __initializer for later use
function wrapInitializer (initializer) {
  var indent = detectIndent(initializer).indent || '  '
  return [
    '__initializer = ( ->',
    indent + initializer,
    indent + 'return this',
    ').call({})'
  ].join('\n')
}

function wrapCode (code) {
  return [
    'return ( -> ',
    code,
    ' ).apply(__initializer)'
  ].join('')
}

function compileNode (node) {
  if (node.code === undefined) {
    return
  }
  // We inject the scope of the initializer if it exists
  // into the function that calls the action code
  node.code = compileCoffeeScript(wrapCode(node.code))
  return node
}

function buildNodeVisitor (visitorMap) {
  visitorMap = visitorMap || {}
  return function (node) {
    var visitor = visitorMap[node.type] || function () {}
    return visitor(node)
  }
}

function compileExpression (node) {
  compile(node.expression)
  compileNode(node)
  return node
}

function compileSubnodes (property) {
  return function (node) {
    for (var i = 0; i < node[property].length; i++) {
      compile(node[property][i])
    }
    return node
  }
}

// Recursively walk through all nodes
function compile (nodes) {
  buildNodeVisitor({
    grammar: compileSubnodes('rules'),
    choice: compileSubnodes('alternatives'),
    sequence: compileSubnodes('elements'),
    semantic_not: compileNode,
    semantic_and: compileNode,
    literal: compileNode,
    rule_ref: compileNode,
    'class': compileNode,
    any: compileNode,
    action: compileExpression,
    rule: compileExpression,
    named: compileExpression,
    labeled: compileExpression,
    text: compileExpression,
    simple_and: compileExpression,
    simple_not: compileExpression,
    optional: compileExpression,
    zero_or_more: compileExpression,
    one_or_more: compileExpression
  })(nodes)
}

function pass (ast) {
  // Add an initializer block if there is none.
  if (!ast.initializer) {
    ast.initializer = {
      type: 'initializer',
      code: ''
    }
  }
  ast.initializer.code = compileCoffeeScript(wrapInitializer(ast.initializer.code))
  compile(ast)
}

module.exports = {
  use: function (config, options) {
    config.passes.transform.unshift(pass)
  }
}