GitHub - dharmatech/2026-09-02-aloe-racket

Scheme is a small gem. Aloe is a similar gem with two new facets.

1. Send, not apply. A list is (receiver selector arg …). The selector is a symbol; it is not evaluated. Functions are objects that understand call.
2. Types, inferred where you do not write them. Classes declare fields and methods. The rest of the program should not repeat those types.

In the 1970s Steele and Sussman studied Hewitt’s actor model and found that message send and function application could express each other. Scheme took application as the primitive. Aloe takes the other branch: a Lisp whose kernel is sending a message.

The core stays small on purpose. Libraries and programs grow the rest (lib/list.aloe, examples/). See docs/philosophy.md and SPEC.md.

ALOE = Scheme + Smalltalk + Types

Status

Aloe 0.2 is an exploratory prototype. The implementation is a definitional interpreter plus a type checker, written in Racket. There is no bytecode VM and no native compiler. Types are checked before evaluation; inference fills in what you do not write.

Layout

• SPEC.md — language 0.1 plus 0.2 additions
• CHECKPOINTS.md — implementation order
• AGENTS.md — rules for a coding agent
• lib/list.aloe — Aloe implementations of fold, reverse, and map
• examples/boids.aloe — target program
• examples/mpl/ — 0.2 computer algebra fragment
• docs/journal/ — release notes

Driver

From the project directory, after loading the Racket path from your profile:

./bin/aloe
./bin/aloe examples/boids.aloe
./bin/aloe --quit examples/boids.aloe

The first command starts the REPL. Loading a file without --quit evaluates it and then opens the REPL with its definitions and classes still available.

0.1 goal

Typecheck examples/boids.aloe and evaluate (demo step).

Interpreter + type checker in Racket only. No compiler.

Legal now: Aloe 0.1 typechecks and evaluates the complete examples/boids.aloe program, including both trailing step sends.

0.2 additions

Aloe 0.2 adds protocols and method overloads. examples/mpl/ is a Cohen-style CAS fragment built around the Math protocol: primitive Int is not Math, so algebraic constants use Num. The default printer sends show when an object provides it, while the REPL command :raw prints the structural #<…> form. To try it, load the MPL core and bind a symbol:

(load "examples/mpl/core.aloe")
(define x (Sym new "x"))