Map and Reduce Monad for Clojure… What about a Juxt Monad?

Question

Whilst learning Clojure, I\'ve spent ages trying to make sense of monads - what they are and how we can use them.... with not too much success. However, I found an excellent \'M

Answer 1

Your questions are not a type of monads. They seems more like a syntactic sugar and that you can accomplish using macros and I won't even suggest you do that because map, reduce etc are simple functions and there is no need to make their interface complex.

The reason these cases are not monads because moands are sort of amplified values which wrap normal values. In map and reduce case the vector that you use doesn't needs to be amplified to allow it to work in map or reduce.

It would be helpful for you to try macroexpand on the domoand expressions. For ex: the sequence monad example should expand to something like:

(bind (result (range 5)) 
   (fn [a] 
      (bind (result (range a))
        (fn [b] (* a b))
   )))

Where the bind and result are functions defined in the sequence monad m-bind and m-result. So basically the vector expression(s) after the domand get nested and the expression(s) after the vector are used as it is in above case the (* a b) is called as it is (just that the a and b values are provided by the monad). In your example of map monad the vector expressions are supposed to be as it is and the last expression (+ a b) should somehow mean (map + a b) which is not what a monad is supposed to do.