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My understanding of a monad is that it isn't currying or recursion though. E: I shouldn't even call it an understanding of monads. I've read at least 15+ expl

• skwosh 11y ago
  Apologies in advance for the unsolicited monad tutorial (it's my turn to be that asshole)... Firstly, saying "`X` is a monad" is the same as saying "class `X` implements the monad interface". The monad interface is usually defined with `return` and `bind`, but I think it's more instructive to borrow the terminology from JavaScript's `Promise`... * `Promise#resolve(value)` is the same as `return`, also known as `pure`. It just wraps the given value in a promise. * `Promise#then(function)` combines both `bind` (when a new Promise is constructed and returned) and the functor method `map` (when a plain value is returned). To provide a unified monad/functor interface for both `Promise` and `Array` (using `wrap` instead of `resolve): // `then` provides both `bind` and `map` depending on the return type of the given function: Promise.prototype.map = Promise.prototype.then Promise.wrap = Promise.resolve // f maps elements to arrays of elements: Array.prototype.then = function (f) { return [].concat.apply ([], this.map(f)) } Array.wrap = function (x) { return [x] } There's no intrinsic value beyond that shared interface, it just allows you to write abstractions without knowing specifically what kind of monad you're dealing with (like the "do" syntax). EDIT: BTW, I've purposely skipped a few things in this description, it's meant to be illustrative, not definitive...