render.js

// var Scope = require('./scope');

function _renderTokens (con_Text, tokens_list, scope, statements) {

  return tokens_list.reduce(function (result, token) {
    if( typeof token === 'string' ) return result + token

    if( !token.$$ ) throw new Error('Unrecognized token type')

    if( !token.$ ) {  // ${ expression } special case
      return result + con_Text.eval(token.$$)(scope)
    }

    if( !statements[token.$] ) throw new Error('Unrecognized command')

    return result + statements[token.$].call(con_Text, token.$$, scope, function renderContent (_scope) {
      if( typeof token._ === 'string' ) return token._
      return _renderTokens(con_Text, token._, _scope, statements)
    }, function renderOtherwise (_scope) {
      if( typeof token.__ === 'string' ) return token.__
      return _renderTokens(con_Text, token.__ || [], _scope, statements)
    })

  }, '')
}

module.exports = function renderTokens (con_Text, tokens_list, data, statements) {
  if( !(tokens_list instanceof Array) ) throw new TypeError('tokens list should be an Array')

  return _renderTokens( con_Text, tokens_list, data || {}, statements || {} )
}