Actors for Smalltalk

About two years ago I wrote an Erlang-style Actors implementation for Squeak Smalltalk, based on subclassing Process, using Smalltalk’s Message class to represent inter-actor messages, and using Promise for RPC. Roughly a year ago, I finally dusted it off, documented it, and released it.

It draws on my experience of Erlang programming in a few ways: it has links and monitors for between-actor failure signalling; it has library actors representing sockets; it has a simple tracing facility. There’s crude and no doubt heavily problematic support for basic Morphic interaction.

Installation instructions, comprehensive documentation and tutorials can be found at

It’s by no means as ambitious as other Smalltalk Actor systems: it only deals with single-image in-image messaging between actors, and doesn’t have the E-style ability to refer to objects within a vat. Instead it follows Erlang in having references denote actors (i.e. vats, roughly), rather than anything more fine-grained.

Next steps could be:

  • a Workspace that was actor aware, i.e. each Workspace an actor.
  • better Supervisors.
  • tools for visualizing the current constellation of actors, perhaps based on Ned Konz’s Connectors?
  • an ActorEventTrace subclass that is able to draw message interaction diagrams as a Morph.
  • a screencast of building an IRC client maybe?

To give it a try:

  1. Download and run a recent version of Squeak. For example, I just downloaded

  2. Update your image. Click the Squeak icon in the top left of the window, and choose “Update Squeak”, or execute the following in a workspace:

    MCMcmUpdater updateFromServer
  3. Install the Actors project into your Squeak:

    (Installer squeaksource project: 'Actors') install: 'ConfigurationOfActors'
  4. Follow the documentation, which includes tutorials of various levels of complexity and a detailed user manual,

It could in principle work in Pharo, as well. I did try to port it to Pharo, but found two main obstacles. First, Pharo doesn’t have an integrated Promise implementation; the Actors project makes heavy use of promises. Second, I couldn’t get Pharo’s sockets to behave as reliably as Squeak’s. I don’t remember details, but I’d be very pleased if a Pharo expert were to have a try at porting the code across.

The project has recently been discussed on HN; please feel free to get in touch if you have any questions, comments or feedback.