An experiment in implementing an IO monad in Clojure. Why should Haskell have all the fun(ctional purity)?

For an in-depth explaination of the motivations and process that went into this, check out my write-up

You probably don't want to use this for any money-making purpose, but it was a lot of fun to write, and hopefully contains some educational value for others.

Include

[pure-io "0.1.0"]
[org.clojure/algo.monads "0.1.5"]

in project.clj

Define an instance of the IO monad

(require '[clojure.pure-io.impl :refer [println' read-line']]
         '[clojure.algo.monads :refer [with-monad]]
         '[clojure.pure-io.monad :refer [io-m]])

(with-monad io-m
  (def echo
    (m-bind read-line' println')))

Peform your IO

(require '[clojure.pure-io.core :refer [perform-io!]])

(perform-io! echo)
;; type "hello"
;; prints "hello"

Bask in the glory of your functional purity

If you're really feeling bold, you can easily define your own pure IO operations using the as-io macro

(require '[clojure.pure-io.core :refer [as-io]])

(defn pure-database-query [query]
  (as-io (some-database-operation query)))

(with-monad io-m
  (def db-read-print
    (m-bind (pure-database-query {:where ...})
            (partial println' "Database query results:"))))

as-io will return the code inside of it as an IO instance, for you to compose as you wish before calling perform-io! on it.

A simple sorting example you can run using cat sample.txt | lein run -m examples.clojure.pure-io.sorting

A more interesting (and fun) guessing game example can be run with lein run -m examples.clojure.pure-io.guessing

Copyright © 2023 Michael Marsh

Distributed under the Eclipse Public License version 1.0