Editing Generator (computer programming) (section)

===Racket===
[[Racket (programming language)|Racket]] provides several related facilities for generators.  First, its for-loop forms work with ''sequences'', which are a kind of a producer:
<syntaxhighlight lang="racket">
(for ([i (in-range 10 20)])
  (printf "i = ~s\n" i))
</syntaxhighlight>
and these sequences are also first-class values:
<syntaxhighlight lang="racket">
(define 10-to-20 (in-range 10 20))
(for ([i 10-to-20])
  (printf "i = ~s\n" i))
</syntaxhighlight>
Some sequences are implemented imperatively (with private state variables) and some are implemented as (possibly infinite) lazy lists.  Also, new struct definitions can have a property that specifies how they can be used as sequences.

But more directly, Racket comes with a generator library for a more traditional generator specification.  For example,
<syntaxhighlight lang="racket">
#lang racket
(require racket/generator)
(define (ints-from from)
  (generator ()
    (for ([i (in-naturals from)]) ; infinite sequence of integers from 0
      (yield i))))
(define g (ints-from 10))
(list (g) (g) (g)) ; -> '(10 11 12)
</syntaxhighlight>
Note that the Racket core implements powerful continuation features, providing general (re-entrant) continuations that are composable, and also delimited continuations.  Using this, the generator library is implemented in Racket.