First draft of R7RS (Scheme) small language available | Hacker News Reader

First draft of R7RS (Scheme) small language available

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36 pointspdelgallego12 comments

Apologies if you receive multiple copies of this message.

Like the other one still on the front page?

http://news.ycombinator.com/item?id=2453832

That is a standard preface for many lists that get a lot of crossposts. You'll see it a lot on most academic mailing lists where conferences and papers are announced and crossposted to many similar lists that receivers may be subscribed to.

I'm aware of its use as a courtesy to the readers. I was amused to see it on something that got posted here multiple times and hoped to let everyone else in on the joke.

Summary : https://groups.google.com/forum/#!topic/comp.lang.scheme/MCf...

What's wrong with R5RS?

It's not as good as R7RS.

The lack of a proper module system was the major drawback for me. I also miss the immutable lists by default that racket provides.

Nothing's wrong with it; it just doesn't go far enough.

It doesn't define a standard module system or macros (beyond syntax-rules), exceptions, or record types. Most R5RS implementations offer those, but they're all different and incompatible. The standard also doesn't help with boring but necessary stuff like file encodings, character sets, etc.

So instead of writing a (nontrivial) program for R5RS Scheme, you have to write it for MIT Scheme or Racket or Chicken or Chibi or ...

What's right, though, is you can implement an interpreter in a weekend. That makes it usable in a lot of places. Once you add exceptions, that goes away. File encodings and character sets are nice, but short-sited. R5RS was eternal. No one predicted the move to Unicode 35 years ago when Scheme was created, and that lack of definition let it make the transition fine.

I'm all for recommendations on things like those, so if you chose to implement them, there's a standard way, but I'm not in favor of making those part of the standard.

Implementing an interpreter for a language in a weekend is a less common need than writing a program for the language. If you want to write an interpreter that does no more than R5RS in a weekend, R5RS is perfect for you. But surely you can see the need for a standard beyond that.

Once you add exceptions, that goes away.

Not really. Exceptions are easy to build on top of continuations, which are already part of R5RS.

The case-folding behavior of the reader can now be explicitly controlled.

Meh.

Module System

Is there a discussion of this somewhere? Why this style of module system?

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