Code examples in the documentation don't return what's expected

[piotr-yuxuan]

Versions used:

• [org.clojure/clojure "1.10.1"]
• [funcool/cats "2.3.6"]
• [funcool/promesa "5.1.0"]

ns form:

(ns user
  (:require
    [cats.builtin]
    [cats.core :refer [bind return alet mlet fmap fapply]]
    [cats.monad.maybe :refer [just]]
    [cats.labs.promise]
    [promesa.core :as p]))

When evaluating the examples provided in https://funcool.github.io/cats/latest/#alet, some results don't match what is shown in the doc:

(macroexpand '(alet [a (just 1)
                     b (just 41)]
                (+ a b)))
;; =>
(fapply
  (fmap
    (fn [a]
      (fn [b]
        (do (+ a b))))
    (just 1))
  (just 41))

;; the documentation suggests it returns:
(fapply (fn [a]
          (fn [b]
            (do
              (+ a b))))
        (just 1)
        (just 41))

The asynchronous code raises an exception:

(defn sleep-promise
  "A simple function that emulates an
  asynchronous operation."
  [wait]
  (p/promise (fn [resolve reject]
               (future
                 (Thread/sleep wait)
                 (resolve wait)))))

(time
  @(mlet [x (sleep-promise 42)
          y (sleep-promise 41)]
         (return (+ x y))))
;; Execution error (ClassCastException) at user/eval34213$fn$fn (user.clj:4).
;; class user$sleep_promise$fn__34206 cannot be cast to class java.lang.Number (user$sleep_promise$fn__34206 is in unnamed module of loader clojure.lang.DynamicClassLoader @571ca823; java.lang.Number is in module java.base of loader 'bootstrap')

Anyway thanks for the work already done on this library!