Derive

Derive is a dependency tracking framework that supports practical Reactive Programming in ClojureScript.

Derive functions behave just like a memoizing function with automatic, behind-the-scenes cache invalidation and upstream notification when dependencies change. Dependencies are captured during the dynamic extent of the function execution for each unique set of parameters. Dependencies are produced by other derive functions and from one or more stores that implement derive's dependency tracking protocol.

The built-in SimpleStore (derive.simple) serves as a working example and NativeStore is the first complete store to participate in the tracking protocol and is focused on efficient indexing and manipulation of native objects.

It should be possible to adapt Dave Dixon's work on Datascript to support the derive model.

Benefits

• Localize the logic specific to deriving and computing "renderable models" to the components that will consume them (instead of in the parent functions or external 'tree construction' logic)
• Derive functions replace the need to compute and manage 'intermediate state' between your server and your render functions
• Automatically notify the UI when the latest data it depended on changed after side effects to the source data are committed to the data store.
• Parents in a render tree need minimal information about the representation manipulated by the child. The data passed in is more like function call parameters than a state model.
• Avoid explicit specification of dataflow; the function call context within the body of a render loop will capture all dependencies.
• Derivation functions become the api to the database.
• Support dynamic programming: only derive a model when the underlying data has changed since the last call. Calling derive functions multiple times is cheap, just like rendering a component in Om is cheap when nothing has changed.

Installing

Add derive to your dependencies.

:dependencies [[com.vitalreactor/derive "0.2.0"]]

Then require it inside your code

(ns foo.bar
  (:require [derive.core :as d :include-macros true]))

(defnd note [store id]
  (transform-note (store id)))

(defnd 

Integration with Om/React

Testing

• Test: lein with-profile test test
• TDD: lein with-profile test cljsbuild auto test

TODO

• Proper tutorial leveraging SimpleStore
• Support explicit invalidation, memoized data TTL or LRU policies on fixed-size DependencyTracker caches (to recover memory in long-running programs), and to make these policies configurable with metadata.
• Utilize speculative parallelism to pre-populate caches. In a threaded platform this reduces to a 'touch' operation running on a background thread. In Clojurescript web workers will require a little more machinery to keep a background DB in sync with the main DB and forward pre-computed state to derive functions on the main thread.

Acknowledgements

This library was written by Ian Eslick and Dan Jolicoeur and benefited from discussions with Ryan Medlin and Dom Kiva-Meyer. We pulled ideas from quite a few other systems, but most heavily from work on Pedestal by Cognitect / Brenton Ashworth and the various React Clojurescript libraries Om/Reagent/etc.