arbitrarily-positioned-threading-macro.clj

;;; First version
(defmacro -<> [subject & body]
  `(let [~'<> ~subject]
     ~(if (empty? body)
        '<>
        `(-<> ~(first body)
              ~@(rest body)))))

(-<> "asdf"
     (.length <>)
     (* 2 <>)
     #(+ 30 <> %)
     (<> 100))
;; => 138

;; To be:
;; (let*
;;   [<> "asdf"]
;;   (let*
;;     [<> (. <> length)]
;;     (let*
;;       [<> (* 2 <>)]
;;       (let*
;;         [<> #(+ 30 <> %)]
;;         (let* [<> (<> 100)] <>)))))

;;; Better version.
(defmacro -<> [& body]
  `(let
       [~@(interleave (repeat '<>) body)]
     ~'<>))

(-<> "asdf"
     (.length <>)
     (* 2 <>)
     #(+ 30 <> %)
     (<> 100))
;; => 138

;; To be:
;; (let*
;;   [<>
;;    "asdf"
;;    <>
;;    (. <> length)
;;    <>
;;    (* 2 <>)
;;    <>
;;    #(+ 30 <> %)
;;    <>
;;    (<> 100)]
;;   <>)