zizzmap

Persistent map with lazily evaluated values for Clojure(Script).

zizz (noun) A nap.

Motivation

• Access map values with delayed evaluation as ordinary map values.
• Pass maps with delayed values to code which should not care that values are delayed.

Features

• Keep pending delayed values not realized until used.
• Do not mix zizzmap-delays with delays created by clojure.core/delay.
• Support IFn interface of persistent map.
• Support transients.
• Transparent IPersistentMap behaviour with minimal overhead.

Where to use

The zizzmap can be used when large map need to be created but most of the map keys will never be used. For example ring request map with multiple conversions from HTTP request to Clojure data structure.

API

init

The macro init is used to define map with delayed values.

(ns project.readme.core-01-init
  (:require [strojure.zizzmap.core :as zizz]))

(def ^:private -map
  (zizz/init {:a (do (println "Init") 1)}))

(get -map :a)
;Init
;=> 1

assoc*

The macro assoc* returns map with delayed value at specified key.

(ns project.readme.core-02-assoc
  (:require [strojure.zizzmap.core :as zizz]))

(def ^:private -map
  (zizz/assoc* {} :a (do (println "Init") 1)))

(get -map :a)
;Init
;=> 1

merge*

The function merge* is like clojure.core/merge but keeps pending values not realized.

(ns project.readme.core-03-merge
  (:require [strojure.zizzmap.core :as zizz]))

(def ^:private -merged
  (zizz/merge* {:a 1}
               (zizz/init {:b (do (println "Init") 2)})))

(get -merged :a)
;=> 1

(get -merged :b)
;Init
;=> 2

update*

The function update* is like clojure.core/update but delays application of function f to map value.

(ns project.readme.core-04-update
  (:require [strojure.zizzmap.core :as zizz]))

;;; Update delayed value

(def ^:private -map1
  (-> (zizz/init {:a (do (println "Init") 1)})
      (zizz/update* :a inc)))

(get -map1 :a)
;Init
;=> 2

;;; Delayed update in standard map

(def ^:private -map2
  (-> {:a 1}
      (zizz/update* :a (fn [a]
                         (println "Update")
                         (inc a)))))

(get -map2 :a)
;Update
;=> 2

Performance

See some benchmarks here.