Generator (computer programming): Difference between revisions

Revision as of 14:07, 9 August 2011

Revision as of 16:18, 18 August 2011

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IO.WriteLn "I=", I

</source>

=== 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:

<source lang="scheme">

(for ([i (in-range 10 20)])

(printf "i = ~s\n" i))

</source>

and these sequences are also first-class values:

<source lang="scheme">

(define 10-to-20 (in-range 10 20))

(for ([i 10-to-20])

(printf "i = ~s\n" i))

</source>

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,

<source lang="scheme">

#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)

</source>

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.

===Tcl===

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[[Category:Articles with example Perl code]]

[[Category:Articles with example Tcl code]]

[[Category:Articles with example Racket code]]

[[fr:Générateur (informatique)]]