setup() {
    var root = this.root;
    var imports = [];

    this.populateGlobalScope();
    this.imports.forEach(function (file) {
      var expr = new nodes.Expression;
      expr.push(new nodes.String(file));
      imports.push(new nodes.Import(expr));
    }, this);

    root.nodes = imports.concat(root.nodes);
  }
Perform evaluation setup:

  - populate global scope
  - iterate imports

@api private