Chained tagged templates

concat.js

function concat(head, template) {
  "use strict";

  var head;
  if(!template) {
      template = head;
      head = '';
  }
  
  var fn = concat.bind(null, head + template[0]);

  fn.toString = function() {
    return head + template[0];
  };

  return fn
}

concat`1``2``abc`.toString(); // 12abc