piping.clj

;; https://stackoverflow.com/questions/24897818/how-to-add-docstring-support-to-defn-like-clojure-macro
(defn resolve-params
  "Takes parameters to a def* macro, allowing an optional docstring and opts by sorting
   out which parameter is which.
   Returns the params, body, docstring, and opts it found."
  [args]
  (let [[docstring args] (if (string? (first args))
                           [(first args) (rest args)]
                           [nil args])
        [params args] [(first args) (rest args)]
        [opts args] (if (associative? (first args))
                      [(first args) (rest args)]
                      [nil args])
        body args]
    [params body docstring opts]))

(defmacro with-cli-pipe-for
  [piped-field-kw [_ fn-name & defn-form]]
  (let [[params body docstring opts] (resolve-params defn-form)
        piped-field (symbol (name piped-field-kw))]
    ;; so that potentially nil opts is removed - hacky
    (remove nil?
      `(defn ~fn-name {:doc ~docstring} ~params
         ;; may result in `nil`
         ~(if opts opts)
         ;; fallback to piping if `piped-field` has no value
         (let [~piped-field (or
                              ~piped-field
                              (do
                                (println "piping!")
                                (line-seq (java.io.BufferedReader. *in*))))]
           ~@body)))))

(do
  (with-cli-pipe-for :workitem-ids
    (defn test1 [{:keys [workitem-ids] :as m}]
      (prn m)
      (run! println workitem-ids)))
  (with-open [is (java.io.StringReader. "1\n2\n3\n5")]
    (binding [*in* is]
      (test1 {:opt1 true})))
  (macroexpand '(with-cli-pipe-for :workitem-ids
                  (defn test1 [{:keys [workitem-ids] :as m}]
                    (prn m)
                    (run! println workitem-ids)))))