A pointed functor is a functor with an
ofmethod
class IO { // The value we take for IO is always a function! static of (x) { return new IO(() => x) } constructor (fn) { this.$value = fn; } map (fn) { return new IO(compose(fn, this.$value)) } }
What‘s important here is the ability to drop any value in our type and start mapping away.
IO.of(‘tetris‘).map(concat(‘ master‘)); // IO(‘tetris master‘) Maybe.of(1336).map(add(1)); // Maybe(1337) Task.of([{ id: 2 }, { id: 3 }]).map(map(prop(‘id‘))); // Task([2,3]) Either.of(‘The past, present and future walk into a bar...‘).map(concat(‘it was tense.‘)); // Right(‘The past, present and future walk into a bar...it was tense.‘)
The benifits using ‘of‘ instead of ‘new‘ is that we can map over the ‘Task.of().map(fn)‘ right away.
Consider this:
const m = new Maybe(1336): m.map(add(1)) //VS Maybe.of(1336).map(add(1));
To avoid the new keyword, there are several standard JavaScript tricks or libraries so let‘s use them and use of like a responsible adult from here on out. I recommend using functor instances from folktale, ramda or fantasy-land as they provide the correct of method as well as nice constructors that don‘t rely on new.
[Functional Programming] Pointy Functor Factory
原文：https://www.cnblogs.com/Answer1215/p/10423882.html