RWExceptionT.clj

  (defn stuff
    [base]
    (m/mlet rwx/rwexception-ctx
      [_ (writer/tell [:base base])

       {offs :config/offset} (reader/ask)
       _ (writer/tell [:config/offset offs])

       tot (m/return (+ base offs))
       _ (writer/tell [:total tot])]

      ;; (throw (ex-info "boo" {}))

      (m/return tot)))

  (defn handle-stuff
    [& args]
    (m/with-context rwx/rwexception-ctx
      (-> (apply stuff args)
          (e/handle
           (fn [left right]
             (if (some? left)
               (m/mlet
                 [_ (writer/tell [:ex :handled])]
                 (m/return (ex-message left)))

               (m/mlet
                 [_ (writer/tell [:ex :none])]
                 (m/return right))))))))

  ;; writer log is preserved through errors,
  ;; and you can log in handle, catch and finally

  (r/run (handle-stuff 100)
    {:monad.reader/env {:config/offset 100}})

  =>

  {:monad.writer/output {:base [100],
                         :config/offset [100],
                         :total [200],
                         :ex [:none]},
   :monad/val 200}