An FRP library for Clojure and ClojureScript
Latest commit 8e43708 May 22, 2014 @weavejester Released 0.10.1


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Reagi is an FRP library for Clojure and ClojureScript, built on top of core.async. It provides tools to model and manipulation values that change over time.


Add the following dependency to your project.clj file:

[reagi "0.10.1"]


Reagi introduces two new reference types, behaviors and event streams, which are collectively known as signals.

user=> (require '[reagi.core :as r])

A behavior models continuous change, and is evaluated each time you dereference it.

user=> (def t (r/behavior (System/currentTimeMillis)))
user=> @t
user=> @t

An event stream models a series of discrete changes. Events must be expicitly delivered to the stream. Dereferencing the event stream returns the last value pushed onto the stream.

user=> (def e (r/events))
user=> (r/deliver e 1)
#<Events@66d278af: 1>
user=> @e

If the event stream is empty (i.e. unrealized), dereferencing it will block the running thread, much like a promise.

Unlike promises, event streams can have more than one value delivered to them, and may be constructed with an initial value:

user=> (def e (r/events 1))
user=> @e

Reagi provides a number of functions for transforming event streams, which mimic many of the standard Clojure functions for dealing with seqs:

user=> (def incremented (r/map inc e))
user=> (r/deliver e 2)
#<Events@66d278af: 2>
user=> @incremented

For a full list, see the API docs.

Event streams can interoperate with core.async channels using port and subscribe. The port function returns a write-only stream that will deliver values to the stream:

user=> (>!! (r/port e) 3)
user=> @e

The subscribe function allows an existing channel to be registered as an output for the stream.

user=> (def ch (async/chan 1))
user=> (r/subscribe e ch)
#<ManyToManyChannel clojure.core.async.impl.channels.ManyToManyChannel@3b4df45f>
user=> (r/deliver e 4)
#<Events@66d278af: 4>
user=> (<!! ch)

Note that this may cause the source stream to block if you don't consume the items in the channel, or provide a sufficient buffer.

Behaviors can be converted to event streams by sampling them at a specified interval in milliseconds:

user=> (def et (r/sample 1000 t))
user=> @et

Signals can be completed with the completed function, which acts in a similar fashion to clojure.core/reduced. Signals that are completed will always deref to the same value. Any values pushed to a completed event stream will be ignored.

user=> (def e (r/events))
user=> (r/deliver e (r/completed 1))
#<Events@66d278af: 1>
user=> (r/deliver e 2)
#<Events@66d278af: 1>
user=> @e
user=> (r/complete? e)


Differences in ClojureScript version

The ClojureScript version of Reagi has two main differences from the Clojure version:

  1. Trying to deref an unrealized stream blocks the current thread in Clojure, but returned js/undefined in ClojureScript.

  2. Event streams that fall out of scope in Clojure are automatically cleaned up. In ClojureScript, the reagi.core/dispose function must be manually called on streams before they fall out of scope.


Copyright © 2014 James Reeves

Distributed under the Eclipse Public License, the same as Clojure.