Multimethods

2023-06-16

Multimethods in Clojure are a way to dispatch function calls based on parameter value.

I use them in my TicTacToe program to easily create different difficulty levels when playing against the computer.

Firstly, I use defmulti to create the multimethod with a dispatch function:

(defmulti get-computer-move (fn [difficulty board] difficulty))

Here we're defining get-computer-move to be a function that takes in two parameters, difficulty and board. We also define the dispatch function to simply return the difficulty. The dispatch function will be how the multimethod determines which method to call.

Next, I define some methods:

(defmethod get-computer-move :hard [_ board]
  #_(...calculate the best move))

(defmethod get-computer-move :medium [_ board]
  #_(...calculate an easier move))

(defmethod get-computer-move :easy [_ board]
  #_(...calculate an even easier move))

The parameter after get-computer-move is the key to which the multimethod will look to find a match with the dispatch function. So if difficulty is :hard, then it will call the first method.