rss-thread-watcher/src/rss_thread_watch/utils.clj

(ns rss-thread-watch.utils
  "Util functions"
  (:gen-class))
;; ===== Generic functions ====

(defn indices
  ;; https://stackoverflow.com/questions/8641305/find-index-of-an-element-matching-a-predicate-in-clojure
  "Returns indexes of elements passing predicate"
  [pred coll]
   (keep-indexed #(when (pred %2) %1) coll))

;; ===== Macros =====
(defmacro nil?-else
  "Return x unless it's nil, the return y"
  [x y]
  `(let [result# ~x]
        (if (nil? result#)
          ~y
          result#)))

(defmacro when-else
  "Evaluates tst, if it's true returns it's result.
   If it's not, return else"
  [tst else]
  `(let [res# ~tst]
     (if res#
       res#
       ~else)))

;; Todo: Test this properly and if working, replace when-else with this
;; Todo: find a way to download clojure documentation for offline use
(defmacro when-else2
  "Evaluates [tst], if it's truthy value returns that value.
   If it's not, execute everything in [else] and return last expr."
  [tst & else]
  `(let [res# ~tst]
     (if res#
       res#
       (do ~@else))))

(defmacro ret=
  "compares two values using [=]. If the result is true
   returns the value, else the result of [=].

   Usefull with if-else"
  [x y]
  `(let [x# ~x
         y# ~y
         result# ~(= x y)]
     (if result#
       ~x
       result#)))