Unless error macro

unless-error.cljc

(defmacro unless-error->
     "Unless expr is a map like {:error xxx}, threads it into the first form (via ->),
     and unless that result is a map like {:error xxx}, through the next etc"
     [expr & forms]
     (let [g (gensym)
           steps (map (fn [step] `(if (:error ~g) ~g (~step ~g)))
                      forms)]
       `(let [~g ~expr
              ~@(interleave (repeat g) (butlast steps))]
          ~(if (empty? steps)
             g
             (last steps)))))

(defn boo [x]
  (println "boo:" x)
  {:error "boo"})

(defn foo [x]
  (println "foo:" x)
  (:name x))

(defn moo [x]
  (println "moo:" x)
  (str/upper-case x))
  
(unless-error-> {:name "trump"} foo boo moo)

(unless-error-> {:name "trump"}
                foo
                (fn [x] x)
                moo)