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How to implement redo statement (as in Perl and Ruby) in Lisp

Code that requires break statements or continue statements in other languages can be done with block & return-from or catch & throw in Common Lisp and Emacs Lisp. Then there is code that requires redo statements, or at least best written with redo. And redo statements don't have to be about loops. How can I do redo in Lisp?

If there was a redo equivalent in Lisp, I think it would work like this: special form with-redo which takes a symbol and forms, and redo which takes a symbol. The form (with-redo 'foo BODY-FORMS...) may contain (redo 'foo) in its BODY-FORMS, and (redo 'foo) transfers control back to the beginning of BODY-FORMS.

Solution

  • In Common Lisp:

    (tagbody
   start
   (do-something)
   (go start))


(dotimes (i some-list)
  redo
  (when (some-condition-p)
    (go redo))
  (some-more))