How is Racket different from Scheme?

scheme lisp racket
mudge picture mudge · Jul 27, 2010 · Viewed 55.2k times · Source

Racket is a descendant of Scheme. How is Racket different than R6RS? What did it add, or take away, or is just different?

I understand that Racket is more than a language, it's a platform for languages. But I'm referring to the main Racket dialect.

Answer

Zorf picture Zorf · Jul 29, 2010

Racket is ultimately based on R5RS, and not R6RS and not a strict superset of either. I don't think it can be called 'Scheme' because it's not backwards compatible with any Scheme standard.

Most implementations offer extensions, but are otherwise backwards compatible, of course, the compiler that comes with Racket can also run in R5RS or R6RS mode. Valid R5/6RS Scheme that runs in racket mode may either be rejected, cause runtime errors, or behave differently than it should. With that said, the main points where it is not backwards compatible are:

  • Racket has no set-cdr! and set-car!, rather set-mcar! which only works on pairs specifically created as mutable.
  • What Racket calls letrec is called letrec* in R6RS and doesn't exist in R5RS, what R5RS and R6RS call letrec doesn't exist in Racket.
  • In Racket, a lot of things are self-evaluating which would raise an error in R5RS, most importantly the empty list.
  • Racket is case sensitive, though R6RS is also case sensitive
  • Racket treats ( ... ) and [ ... ] as equivalent, R5RS does not, but R6RS does.

There are probably more, but on most other parts racket is a superset of Scheme.

Related questions

What is the best Scheme or LISP implementation for OS X?

I am looking for a version of Scheme or even LISP that I can use to recover some lost Lisp development skills. Some web capabilities would be nice but not essential. I've looked at Plt and MIT scheme and, while …

Read More
What are the differences between Clojure, Scheme/Racket and Common Lisp?

I know they are dialects of the same family of language called lisp, but what exactly are the differences? Could you give an overview, if possible, covering topics such as syntax, characteristics, features and resources.

Read More
What are the actual differences between Scheme and Common Lisp? (Or any other two dialects of Lisp)

Note: I am not asking which to learn, which is better, or anything like that. I picked up the free version of SICP because I felt it would be nice to read (I've heard good stuff about it, and I'm …

Read More