Dylan is alive and well today, but it has a long history.

Dylan was created in the early 1990s. It was originally a project within Apple Computer, but was expanded to a partnership between Apple, Harlequin and Carnegie Mellon University (CMU).

The original Dylan is now referred to as “Prefix Dylan” and used a traditional Lisp-style syntax:

(define-method sum ((numbers <sequence>))
  (reduce1 + numbers))
(define-method square ((x <number>)) (* x x))
(define-method square-all ((coords <sequence>))
  (map square coords)
(define distance (compose sqrt sum square-all))

Wikipedia also provides a history of the Dylan programming language which provides additional information not included here.

Apple Dylan

At this time, the primary implementation of Dylan was Apple Dylan. While Dylan was originally intended for use on the Apple Newton platform, that didn’t work out and their focus shifted to Dylan on the desktop on classic Mac OS.

Some years ago, Paul R Potts wrote about his experiences with Apple Dylan, including some screenshots. Apple distributed a brochure at WWDC in 1994 (PDF) that described Dylan and the features that it was going to bring to the developer experience.

Change in Syntax

In late 1993 or 1994, CMU and Apple decided to change the Dylan syntax to what we currently have now, the infix syntax. The value of this change was a subject of much debate, both at the time and in the subsequent years. At the time, it was thought that the world wasn’t ready for a mainstream language with a Lisp syntax, so a more familiar syntax might be better. There were also discussions at the time of supporting both the prefix and the infix syntax within the same compiler, something which never came to fruition.

Harlequin Dylan

Sometime in 1993, Harlequin started a project to produce a Dylan development environment, DylanWorks. Harlequin, at the time, was known for their LispWorks product. Keith Playford was their first hire to work specifically on the Dylan project. Keith had previously been involved with EuLisp.

Harlequin’s Dylan was originally implemented using the prefix syntax and later converted to the current infix syntax. The first implementation was a Dylan emulator running on top of LispWorks as described in this Hacker News comment:

When Harlequin started out with Dylan, to bootstrap we first quickly morphed LispWorks into a high-functioning Dylan IDE. This was done through a combination of macro, reader macro and CLOS MetaObject Protocol abuse, allowing us to achieve a faithful rendition of Dylan’s syntax and object system semantics respectively.

When Dylan went from prefix to infix syntax the reader macro indirection got all the more elaborate: what started out as a trivial reader macro that treated colons differently started delegating to a full-blown lex & yacc style parser instead.

All the better, most of this was achieved modularly: Lisp editor buffers and Lisp listeners would run happily alongside Dylan editor buffers and Dylan listeners, Lisp code could still compile load and run alongside Dylan code, and Lisp classes could interoperate cleanly with Dylan classes.

This emulator can be found in an old revision of Open Dylan’s git repository.

While DylanWorks ran on multiple platforms, the commercial goal was to ship a full development environment on Windows. Unfortunately, at the time, LispWorks did not yet run on Windows and there were goals that were difficult to achieve with LispWorks (like producing native shared libraries and executables). Work began to replace the original emulator with a full-blown compiler and code-generator written in Dylan.


HARP is the Harlequin Abstract RISC Processor and was designed and developed at Harlequin in the late 1980s. It was used in Harlequin’s LispWorks and later translated to Dylan for use in Harlequin’s DylanWorks (which is now Open Dylan).

Clive Tong, an engineer at Harlequin in 1989, briefly described it as:

The compiler targeted an instruction set known as HARP (Harlequin Abstract RISC Processor), and then HARP instructions were translated into machine instructions using a template matching scheme. HARP had an infinite set of registers, and the register colouring happened as part of this templating processing.

Some additional details about the early design of HARP are available in Techniques for Dynamic Software Migration from 1988. Other early sources of information about it, written by Hunter and Knightbridge, appear to be lost to the sands of time.


DFMC (Dylan Flow Machine Compiler) was the Dylan compiler that resulted from the work at Harlequin on DylanWorks. (There were other earlier compilers.) This is the compiler that is still in use today in Open Dylan.


Scott McKay, formerly of Symbolics, produced a cross-platform GUI toolkit for DylanWorks called DUIM, or the Dylan User Interface Manager. This was based on his previous work on CLIM, which in turn was based on Dynamic Windows from Symbolics. While CLIM was the result of collaboration between multiple Lisp companies, DUIM was the work of Harlequin and drew heavily upon the CLIM design.

DUIM is the basis for the Open Dylan IDE. Unfortunately, only the Windows backend for DUIM remains functional.

DUIM documentation can be found amongst the Open Dylan documentation.


Scott McKay also worked on the Deuce editor that was used in the DylanWorks IDE. He wrote about it briefly in a newsgroup posting. Bruce Mitchener also wrote briefly about the architecture of Deuce on the Atom editor discussion forums.

Memory Pool System

The Memory Pool System garbage collector was originally written for DylanWorks and subsequently re-used in other projects. It lives on today as a separate product (and is still used by Open Dylan).

Harlequin’s Demise

Unfortunately, for a variety of reasons, Harlequin fell upon hard times. A group of Harlequin employees started a company Functional Objects and re-named Harlequin DylanWorks to Functional Developer and attempted to continue the development.

Open Sourcing

In 2004, Functional Objects decided to open source the Functional Developer code. It was adopted by an open source community and renamed Open Dylan. Open Dylan development continues today.

Gwydion Dylan

In 1993, Carnegie Mellon University kicked off a project to create a new Dylan implementation, the Gwydion Project. The team at CMU had previously done extensive work in the Lisp field including work on Spice Lisp which evolved into CMUCL. This team was led by Scott Fahlman.


The Gwydion team first produced a Dylan environment known as Mindy or Mindy Is Not Dylan Yet. This compiler was used to bootstrap the subsequent d2c compiler and supported a subset of the full Dylan language. Notably, it did not support macros.


The Gwydion team’s main Dylan implementation work was focused on d2c, an optimizing Dylan compiler that generated C code which could then be compiled to native code.

Gwydion’s Demise

The Gwydion team ceased their work on Dylan due to lack of funding and other concerns.

Scott Fahlman announced that Dylan was in the hands of Harlequin in a September 1998 newsgroup post.

The Gywdion Dylan implementation at that point had already been picked up by an open source community, led by Eric Kidd and Andreas Bogk.

Open Source

In the late 1990s, a group of programmers took over the maintenance and development of the Gwydion Dylan implementation. They continued this development for almost 15 years until the Gwydion Dylan compiler was retired in favor of a focus on the Open Dylan compiler.

The Open Dylan compiler was the result of the open sourcing of the Functional Developer (previously Harlequin DylanWorks) compiler in 2004. Development on Open Dylan continued in parallel with Gwydion Dylan until 2012, when it became the focus of the Dylan hackers.

Other Implementations

Over the years, there have been a variety of other Dylan implementations.

  • In 1992, Digital Equipment Corporation (DEC) had an implementation, Thomas, of the original prefix Dylan, written in Scheme, running on top of Gambit Scheme. One of the authors wrote about his experiences with creating Thomas.
  • In 1994, Jonathan Bachrach had an implementation written on top of CMUCL using a set of macros. This implementation has been lost.
  • The Marlais implementation was abandoned in 2001.
  • Dominique Boucher wrote IDyl, a Dylan interpreter in Scheme in the mid-1990s.
  • RScheme is Scheme-like language perhaps inspired by Dylan. There was some interest in Dylan from UTexas and Paul R. Wilson, but it isn’t clear from the remaining historical data what exactly happened.