function printImports(trees) {
  var names = Object.keys(trees);
  util.print('import {');
  names.forEach(function(name) {
    util.print('  %s,', name);
  });
  util.print("} from '../syntax/trees/ParseTrees.js';")
}
@fileoverview This file generates the code for ParseTreeTransformer.js
based on a JSON file, which gets passed in on the command line.