Why not Haskell syntax?

monad.clj

(ns gist.monad
  (use [clojure.algo.monads :only [domonad]]))

(def <-)

(defn transform-monad-syntax [body last-was-assign]
  (let [[v o e & r] body]
    (cond (empty? body)
          (if last-was-assign
            (throw (IllegalArgumentException. "last value in m-do must be expression"))
            [])

          (= o '<-)
          (concat [v e] (transform-monad-syntax r true))

          :else
          (concat ['_ v] (transform-monad-syntax (rest body) false)))))

(defmacro m-do [monad & body]
  `(domonad ~monad
            ~(vec (transform-monad-syntax body false))
            ~(last body)))