Sample of using funcool/cats {:mvn/version "2.3.2"}

cats.clj

(ns kondo.cats
  (:require
    [cats.core :as m]
    [cats.monad.either :refer [left left? right right?]]))

(defn assoc-b
  [m v]
  (right (assoc m :b v)))

(defn merge-2
  [m m1 m2]
  (right (merge m m1 m2)))

(defn thread-first
  []
  (m/->= (right {})
         (#(right (assoc % :a :b)))
         (assoc-b :c)
         (merge-2 {:c :d} {:d :e})))

(defn assoc-b-last
  [v m]
  (right (assoc m :b v)))

(defn thread-last
  []
  (m/->>= (right {})
         (#(right (assoc % :a :b)))
         (assoc-b-last :c)
         (merge-2 {:c :d} {:d :e})))

(defn thread-as
  []
  (m/as->= (right {}) xxx
           (#(right (assoc % :a :b)) xxx)
           (assoc-b-last :c xxx)
           (merge-2 xxx {:c :d} {:d :e})))