7 x R7RS

14/09/2017

The nice thing about Scheme is that not only it comes in more than seven standards[1], but with tons of implementations as well. I’ve heard from various people that R7RS-small is good enough to write portable code in it that will work on more than one implementation, so I decided to try implementing MAL in it. This has been mostly successful as I’ve started out with 11 implementations, narrowed it down to 7 and found a new one for future experimentation. During this time I’ve reported 14 bugs for two implementations, Cyclone and Foment. My impressions of the implementations can be summarized as follows:

Chibi
The recommended implementation if you’re looking for a fully standards-compliant one. It comes with its own comprehensive test suite that has been borrowed by others. I’ve had zero issues with it, although the overall speed could be better, earning it the last place in the toy benchmarks (where it’s tied with Foment). This is somewhat weird considering that it’s advertised as small yet embeddable (look at Lua for an example of a fast one in that domain); Picrin would be another candidate for that purpose.
Kawa
It proudly wears the GNU banner (despite not being the Scheme officially endorsed by GNU), but is otherwise completely unknown. This is a shame because unlike the other JVM languages I’ve worked with it comes with a fast compiler, has a small boot time and didn’t pose any issues for me, other than having to learn how this classpath thing works in Java. Speed is decent as it comes third place in the toy benchmarks, interop doesn’t look painful either. Its author did a few more interesting things with it, such as implementing other languages like Emacs Lisp (which forms the basis of JEmacs). I might just as well invest more time into it and use it to write things where Clojure would otherwise be a bad idea.
CHICKEN
My favorite implementation for writing all kinds of small, standalone programs. I occasionally stumble upon issues, but none for this run. It’s not completely obvious how to create R7RS programs using libraries from anywhere else than the current directory, this will be hopefully addressed in the next major release, among with a more R7RS-like reorganization of the namespaces and improvements to the package system. Speedwise it’s the best, despite the r7rs egg being known for incurring a huge speed penalty in numerical benchmarks.
Gauche
The domain says it all. I haven’t expected it to support R7RS considering how long it has been around, but it does! Thanks to this it contains many contrib libraries and performs fairly well for an interpreter-only system. If I hadn’t discovered CHICKEN, this might have been my preferred Scheme to go for.
Picrin
The other contender in the embeddable domain. Unfortunately I ran into several problems, the most problematic ones being that it’s currently not buildable from master and that there are no official plans to support loading user-written libraries. For this reason I wouldn’t recommend using it over Chibi.
Sagittarius
A fork of Gauche with more features, some changes (build system, command-line switches) and a bit of performance improvements.
Cyclone
Judging from the design documents this is basically CHICKEN, but with a different approach to GC and threading that allows it to do native threads. It’s a relatively young project and therefore bound to have countless bugs, yet it’s second place in the speed department.
Foment
Someone’s personal project for learning Scheme. It’s about the same speed as Chibi and not quite finished yet.
Guile
The Scheme officially endorsed by GNU. It had a long time in making, but its R7RS support is minimal and only covers reader adjustments.
Racket
I’m somewhat surprised there is unofficial support for R7RS, given that the language itself has been derived from R6RS. Not tested yet.
Larceny
Research project that supports R5RS, R6RS and R7RS to varying degrees. Due to R7RS incompatibilities, a somewhat outdated documentation and a ridiculous toolchain, I’ve decided to test it at some later point to see whether it becomes the fastest implementation for MAL.
Gerbil
I’ve learned about this one from a blog post by Fare, the maintainer of ASDF, a build system for CL packages. It turns out that not only he likes Racket, no, he also switched to this Scheme implementation because it’s made by a close friend who not only ported Racket’s module system to Gambit, but also added R7RS support to it. I expect it to become usable soon and to make for another contender to the fastest Scheme implementation for MAL.
[1]Additionally to RnRS there’s the IEEE standard (which mostly resembles R5RS) and the upcoming R7RS-large standard that aims at giving Scheme a big standard library.