let-else example

(defn search-weather [qparams remote-addr]
  ; three search methods are supported:
  ;   zipcode=XXXXX      return airports within proximity to zipcode
  ;   geo=lat,lon        return airports within proximity of coords
  ;   ip=XXX.XXX.XXX.XXX airports within geolocation of IP address
  ;   ip=@detect         airports within geolocation of client IP
  (when (= (get qparams :ip) "@detect") (assoc qparams :ip remote-addr))
  (let? [geoloc   (get-location qparams)                    :is-not nil? :else (error-response "could not find location")
         stations (db/find-stations (qparams :type) geoloc) :is-not nil? :else (error-response "no stations found for location")
         reports  (if
                    (= (qparams :type) "metar")
                    (reports/get-metars stations)
                    (reports/get-tafs stations))            :is-not nil? :else (error-response "No reports found")]
        (geo-response reports geoloc)))