They aren't planning to add collection methods, just to provide a means for existing methods like Array#map and Array#filter to be typed. Right now there is no

They aren't planning to add collection methods, just to provide a means for existing methods like Array#map and Array#filter to be typed. Right now there is no way to write a type signature that says, given an array of numbers and a function from numbers to strings, Array#map returns an array of strings. This allows that.