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Robin

Version 0.7. Work-in-progress, subject to change.

Overview

Robin is an excessively principled and thoroughly specified functional programming language with eager evaluation, latent typing, and a homoiconic syntax, based on a radically simple core semantics in which the macro, rather than the function, is the fundamental abstraction.

Expressions in Robin are referentially transparent; programs interact with the outside world through a reactive framework.

For more information, see the extended description below.

Quick Start

The Robin reference interpreter is written in about 1300 lines of Haskell. To use it, you'll need an implementation of Haskell installed (typically either ghc or Hugs).

If you have shelf installed, you can just run shelf_dockgh catseye/Robin.

If not, you can clone this repository, cd into the repo directory, and run

./build.sh

to build the reference interpreter. (If you don't have ghc, no executable will be built, but the bin/robin script will use runhaskell or runhugs instead.)

You can then run it on one of the example Robin sources in eg like so:

bin/robin eg/hello-world.robin

You should see

Hello, world!

To continue learning to program in Robin you can follow The Robin Tutorial.

Testing

If you have a few minutes to spare, and you have Falderal installed, you can run the test suite (consisting of more than 400 unit tests) by running

./test.sh

The tests that use only Robin's core semantics (--no-builtins flag) are quite slow, so you may want to skip them. You can skip them by running

APPLIANCES="appliances/robin.md" ./test.sh

The test suite will also run some property tests (using QuickCheck). Notably, for every macro that is defined multiple times (which includes much of stdlib, where the core definitions are written in Robin but also implemented in Haskell as "builtins" in the reference interpreter), QuickCheck will attempt to falsify the assertion that the definitions define the same macro. These attempts are currently rather crude; there is lots of room for improvement for them in some future release.

Extended Description

For experienced programmers, Robin might be best described by listing the languages that have had the strongest influences on it:

Scheme

Like Scheme, Robin is eagerly evaluated, latently typed, and homoiconic, as well as properly tail-recursive and lexically scoped (at least by default), and tries hard to be well-defined and system-agnostic, but (as you can read below) diverges significantly from Scheme in other ways.

Forth

Like Forth, Robin has a radically simple core semantics. There are 15 intrinsic operations; every symbol in the standard library is defined in terms of these intrinsics, while an implementation is free to provide its own (perhaps more efficient) implementation of any such symbol. (See also Pixley).

PicoLisp

PicoLisp allows defining functions with unevaluated arguments. Robin adopts this kind of function for the basis of what it calls a macro, and builds everything else on top of macros. (There is a function form in Robin, but it's defined as a macro!) This is much like how the Kernel programming language builds everything from fexprs; however, Robin was developed oblivious of Kernel — it adapted the idea directly from PicoLisp.

Haskell

Like Haskell, Robin is referentially transparent (often described as "purely functional") — mutation of values is forbidden. (Robin intentionally does not, however, adopt lazy evaluation or a static type system.)

Elm

Reactive programs in Robin are built by composing transducers which are driven by events and produce effects (which are modelled as further events), in a manner very similar to The Elm Architecture.

Bourne shell

Arbitrary text can by embedded in a Robin program using a syntax very much like a "heredoc", except it is an S-expression.

English

Deserves at least a passing mention here, as one thing that Robin discards from Scheme is its jargony terminology: no cdr, no cons, no lambda.

For a full description of the Robin language, see the Robin specification document.

Repository Layout

  • appliances/ — test appliances for the literate test suite.
  • bin/ — driver script, destination for executable when built.
  • demo/ — contains HTML5 document demonstrating build to JS by Haste.
  • doc/ — Tutorial, specification, rationale, etc.
  • eg/ — example programs written in Robin
  • src/ — Haskell source for reference interpreter.
  • stdlib/ — normative definitions of standard library symbols.
  • HISTORY.md — history of this distribution.
  • TODO.md — plans.