Primer

Primer is a pedagogical functional programming language. This repository contains Haskell implementations of:

• the core language;

• database adapters for storing Primer programs in a relational database; and

• a web service, or backend, which exposes a comprehensive programming language API to a client application, or frontend.

A companion repository, primer-app, contains a web-based frontend application for reading, writing, running, and debugging Primer programs.

Both projects are licensed under the terms of version 3 (or later) of the GNU Affero General Public License, and can be freely copied, modified, and distributed, so long as the license is preserved.

Important caveats

Both this implementation of the Primer programming language and the language specification itself are still under heavy development. If you use this implementation, you should expect lots of breaking changes until we reach a 1.0 release.

For a very rough roadmap, see our project milestones. Please note that we don't currently have any accurate time estimates for when we expect these milestones to be reached, and the milestones are subject to change.

Please also read the following important caveats about the current state of the project:

• There is no authentication (authn) system yet, nor an authorization (authz) system, so we strongly recommend that you not host a public Primer service until one or both of those systems are in place. It's safe to experiment with on a local system, or behind a robust identity-aware authentication proxy with a trusted audience, but if you host it publicly, be aware that anyone can read, modify, and delete any existing program; create new programs; and potentially DoS the server on which it runs.

• The current implementation of the step evaluator is very slow. Running very large programs, or even small programs that generate many reduction steps, is not practical at this time. Primer now also features an interpreter which is up to a few orders of magnitude faster than the step evaluator, but we lose the ability to step through programs redex-at-a-time as we can with the step evaluator. We plan to do future research to attempt to combine the two approaches somehow.

• Even the most minor frontend requests result in the entire program AST being sent over the network, rather than only what's changed. This is an obvious area for improvement, and we're certain that we can drastically reduce the amount of data being sent to the client application — we just haven't had a chance to prioritize this work yet. For now, however, please keep a very close eye on your network traffic if you're communicating with the Primer language server over a metered network connection, as the traffic can quickly add up.

• The Haskell API, HTTP APIs, and database schema are all very unstable, and guaranteed to change in compatibility-breaking ways before we reach a 1.0 project milestone.

• The language's semantics are still not fully baked, and there may be defects in its design and/or implementation, so existing Primer programs will probably break from time to time, with no guaranteed forward/backward compatibility path. In other words, you may lose work due to incompatibilities between old Primer programs and new releases of the language. Once we reach version 1.0, we'll only make breaking changes when absolutely necessary, and do our best to provide backward compatibility with existing programs, and/or ways to migrate old programs to the new semantics.

• At the moment, Primer is a pure functional programming language, with no effects system. This means, for example, it's not currently possible to draw animated cats using Primer. We're currently undecided on whether to add an effects system to version 2.0 of the language, or to eschew language-level effects entirely in favor of a different approach more suited to novices.

• We've yet to do any rigorous testing of Primer with students, and none at all in classrooms. Primer may turn out not be an effective way to teach functional programming to novices! That said, if you're an educator and you'd like to know more about the limited testing we have done to date, please reach out to us.

Contributing

We welcome contributions from the community! Please read our contributing guide if you think you'd like to help.

We also provide a comprehensive development guide for anyone who'd like to build and run the project locally.