This pattern helps to convert a connected resource (i.e. a resource accessed via some kind of connection) into a lazy sequence. The idea is to fill a in-memory buffer with data from a connection that is opened and closed. Then consume of the buffer, and when the buffer is empty fill it again with another connection.

Buffered IO - DB - Stream PATTERN

(defn buffered-select [f-select init-pos]
  "Creates a lazy sequence of messages for this datasource"
  (letfn [  
           (m-seq [buff pos] 
                   (if-let [buff2 (if (empty? buff) (f-select pos) buff)]
                         (cons (first buff2) (lazy-seq (m-seq (rest buff2) (inc pos) )))         
                     )
                   )
           ]
    (m-seq nil init-pos)
    )
  )

Usage:

(defn select [pos](range pos))

(def l (buffered-select select 1))

(take 20 l)