code: function exec (opts, cb) {
      var file, ctx;
      if (typeof opts === 'string') {
          file = opts;
          ctx = null;
          opts = {};
      } else {
          ctx = opts.ctx || null;
          file = opts.file;
      }
  
      // caching
      var ctxHash = ctx ? md5(ctx) : '';
      if (!opts.force && exec.cache[file] && exec.cache[file][ctxHash]) {
          process.nextTick(function () {
              cb(null, exec.cache[file][ctxHash]);
          });
          return;
      }
  
      load({file: file, force: opts.forceLoad}, function (err, content) {
          if (err) {
              cb(err);
              return;
          }
  
          var module = _assign({
              Vow     : VOW,
              console : console,
              require : require
          }, ctx);
  
          try {
              VM.runInNewContext(content, module, file + '.vm');
          } catch (e) {
              cb(e);
              return;
          }
  
          // caching
          exec.cache[file] = exec.cache[file] || {};
          exec.cache[file][ctxHash] = module;
  
          cb(null, module);
      });
  }
docs: Caching loader some native file
  @param {String|{file: String, force: Boolean, ctx: Object}} opts filename or object
  with filename, context and options
  @param {Function} cb