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Scheme

Scheme is a Lisp dialect created in 1975 by Guy Steele and Gerald Sussman at the MIT. Scheme is minimalistic and elegant leaning towards a functional programming paradigm, being the language used in the famous SICP book (using the MIT/GNU Scheme implementation).

Scheme is standardized in a series of documents called Revised^n Report on the Algorithmic Language Scheme (RnRS) (where the n stands for the version), being the most popular the R5RS revision released in 1998.

Controversy around the R6RS revision (The Great Bloatening)

In 2003 work in a new revision of Scheme began, R6RS, finished in 2007. This new revision was controversial since it added additional features that Scheme hackers deemed as a departure from Scheme's minimalism. In a attempt to amend this, work on R7RS began, splitting Scheme into two different (but still similar) languages, differing in the amount of features; a big language for practical use and a small, minimalistic version. Of course R7RS is still less bloated than Common Lisp and other mainstream languages.

Scheme Requests for Implementation (SRFI)

Aside from the RnRS, Scheme is also informally standarized by the SRFI, in which extensions to Scheme are discussed, mainly libraries. Some SRFIs are:

Unlike the revisions, these aren't hard requirements to implement, so Scheme implementations are free to implement them or not.

Implementations

Since Scheme (specially the R5RS standard) is simple, there are multiple implementations:

Examples

Hello World

(display "Hello, Scheme!")

Factorial

(define (fact n acc)
  (if (zero? n)
   acc
   (fact (- n 1) (* acc n))))

(let ((ns '(4 0 5 10 1)))
  (for-each (lambda (n)
             (display n)
             (display "! = ")
             (display (fact n 1))
             (newline))
            ns))

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