code: function filterGenerator(filter) {
  	if(typeof filter === "boolean")
  		return () => filter;
  
  	if(typeof filter === "function")
  		return filter;
  
  	if(filter instanceof RegExp)
  		return input => filter.test(input);
  
  	if(filter instanceof Set)
  		return input => filter.has(input);
  
  	if(filter instanceof Map)
  		return input => !!filter.get(input);
  
  	if(Array.isArray(filter))
  		return input => filter.indexOf(input) !== -1;
  
  	if(filter && typeof filter === "object")
  		return input => !!filter[input];
  
  	throw new TypeError("Invalid filter type.");
  }
docs: Generates a filter function out of the given filter.
  @param {any} filter The filter.
  @return {function} A filter function for `filter`.