Panicz Godek is the author of "A Pamphlet Against R" and long time Schemer. In this interview he will tell us what makes his favorite language so special. He will also educate us about his idea of a "Wikipedia for Code."
I have discovered Scheme through Guile, the official extension language of the GNU project. I was developing my own 3d game engine in C++ and I was looking for a language for writing in-game scripts. The way Guile was advertising itself made me believe that it is a good idea to use it that way. This was around 2008, so I could say that I have 10 years of experience working with Scheme. But my style of programming has changed a lot, and it took me some time to learn to appreciate functional programming.
To me, the most important "selling point" of Scheme is its ultimate simplicity. I have used quotation marks here, because it seems to me that not many people buy this, because they don't understand it - probably because they weren't giving it too much thought. Scheme has a reputation of being impractical, and I think that this reputation has been deserved. For example, there hasn't been a standardized module system for many years, and now there are two incompatible "standardized" module systems, so the maintainers still don't know how to package their software to make it portable.
I am aware that this caveat doesn't make "selling" Scheme any easier, so perhaps it is indeed better to focus on the simplicity. In addition to function calls, the functional subset of the Scheme grammar consists only of four special forms: lambda, if, define and quote. Most other things can be constructed as macros. Extending these primitive forms with set!, begin and call/cc turns Scheme into an imperative language. The rest is just function calls.
When I look at macro systems in languages such as Elixir or Scala, I usually wonder why people are so stubborn to making things more difficult to themselves. Of course, the answer is rather simple: people are just unfamiliar with things that they weren't taught at school, which probably makes them feel uncomfortable with them. Also, Scheme isn't a good pen-and-paper notation, and it is more comfortably used on a computer, preferably with editing programs that support s-expressions well. The cognoscenti are probably thinking "Emacs" right now, but unfortunately it isn't a particularly beginner-friendly tool. But I seem to have departed from your question a bit.
Previously you mentioned things like incompatible module systems and these do indeed make selling a language more difficult. The Prolog language suffers from the same problem, however a large amount of Prolog programmers agree on using one non-standard implementation, SWI Prolog, and its Quintus-like module system.
Very good question. I don't think that settling on one implementation is likely, given that "every Scheme user and their grandma" rolls up their own implementation, often with some platform-specific extensions (like Kawa, Biwa, IronScheme or ARMPIT). Also, my impression is that Scheme doesn't have a community (but it used to). There are implementations, such as Racket, Chicken, Guile or Gambit, that gather some communities around them, but I guess that this atypical situation can be confusing to the newcomers to the Scheme world. Of course, there are annual Scheme workshops, but they are rather elitist and esoteric. Also, I think that many people may find the lack of the figure of the "Benevolent Dictator for Life" confusing, and I think that this actually requires more maturity from each single member of community, than having an authoritative figure. Perhaps the role closest to BDFL is currently played by Daniel Friedman, but he's an inspirer rather than a dictator.
I think that the true power of Scheme is that it allows to write very readable code, and perhaps instead of a universal module system, we should have something resembling Wikipedia, but containing only Scheme function definitions (and assertions and examples). I think that the idea of using a programming language for representing general human knowledge has a lot of potential that hasn't yet been exploited.
That indeed is a very interesting idea with implications yet to be found out. Scheme is a descent choice for such a project as it excels at representing certain kinds of human knowledge, but other - at least by default - not so much, e.g. static type information.
I have been devoting a lot of my thinking to this subject, and I have to admit that I do have an "ontological" problem with types. The general idea around Scheme - that we form structures to which we provide interpretations - seems clear and, in a sense - necessary. But every type system that I have seen made an impression that it is somewhat contrived. For example, Haskell's type system seems very elegant on the surface, and is very useful in many situations, but it quickly turns out that it only allows to express a certain set of properties conveniently, and others either can't be expressed at all, or expressing them is so complicated, that interpreting their expression gets really cumbersome. Then there are some extensions to the Haskell's type system, and they all seem rather arbitrary, which makes me think that they are a source of accidental complexity in programming languages, which I find rather off-putting.
It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures.
By contrast, I really appreciate the Boyer-Moore theorem prover, which is a universal language for expressing "static properties" of programs, and it's the very same language that is used for expressing the actual programs.