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The Post-Redirect-Get Pattern

Problem

When displaying a page after receiving a form submission, the browser's "refresh" button should not repost the form results.

Solution

The "Post-Redirect-Get" pattern, or PRG, is a popular web pattern for displaying a page after receiving a form ("POST") submission. The only action performed by the response to form submission is to redirect to an ordinary ("GET") page. This can be abstracted particularly nicely in PLT Scheme with a simple macro redirect/get, which causes its subexpressions to be evaluated in the context of a redirected GET page:

(define-syntax redirect/get
  (syntax-rules ()
    [(_ e ...)
     (send/suspend/dispatch
       (lambda (embed/url)
         (redirect-to (embed/url (lambda (_) e ...)))))]))

Discussion

This solution makes use of the send/suspend/dispatch procedure discussed in WebDispatchOnLink. Note that in recent version of PLT Scheme, this procedure is included in (lib "servlet.ss" "web-server").

See also:

http://www.theserverside.com/articles/article.tss?l=RedirectAfterPost

Comments about this recipe

Contributors

-- DaveHerman - 30 Sep 2005