fell's Introduction

Fell

Freer monads for Clojure and funcool/cats based on Freer Monads, More Extensible Effects and Effect Handlers in Scope.

Usage

Don't.

(ns fell.example
  (:require [cats.core :refer [mlet return]]
            [fell.core :as fell :refer [request-eff]]
            [fell.reader :as r]
            [fell.state :as state]))

;; Workaround for lack of parametric modules.
;; Could use singletons instead, but fn usages would be more verbose.
(let [{ask :ask, run-reader :run} (r/make ::reader)]
  (def ask ask)
  (def run-reader run-reader))

(let [{get-counter :get, set-counter :set, run-counter :run} (state/make ::counter)]
  (def get-counter get-counter)
  (def set-counter set-counter)
  (def run-counter run-counter))

(let [{get-status :get, set-status :set, run-status :run} (state/make ::status)]
  (def get-status get-status)
  (def set-status set-status)
  (def run-status run-status))

(def stateful-computation
  (mlet [initial-status get-status
         counter get-counter
         increment ask
         _ (set-counter (+ counter increment))
         counter* get-counter
         _ (set-status (str "Energy: " counter))]
    (return initial-status)))

(-> stateful-computation
    (run-counter 8)
    (run-reader 17)
    (run-status "Asleep")
    fell/run) ;=> #<Pair ["Energy: 8" #<Pair [25 "Asleep"]>]>