i use clojure and korma libs.

defn db-search-users
  [& {:keys [nick_name max_age min_age page page_size lmt oft]
      :or {lmt 10  page_size 10 oft 0 }
      :as conditons}]
  (let [users-sql  (-> (select* users)
                       (fields :user_name :id :nick_name)
                       (limit (if (nil? page) lmt page_size))
                       (offset (if (nil? page) oft (* page page_size))))]
    (do
       (exec (-> users-sql
                need_do_something_here
             )
       )

  )

now i need to add some search conditions to users-sql at 
"need_do_something_here",i can describe it in imperative style:

if ( nick_name != nil)
    users-sql = (where users-sql (like :nick_name nick_name)
if (max_age != nil)
    users-sql = (where uses-sql (> :birthday blabla....))
if (min_age != nil)
    users-sql = (where uses-sql (< :birthday blabla....))

how to do this in an elegant way with functional style?

another question is: i think code like: (if (nil? page) lmt page) is ugly. 
is there some functions in clojure like (get_default_value_3_if_a_is_null a 
3) ?

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