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List:       sbcl-devel
Subject:    Re: [Sbcl-devel] exporting merge-tail-calls from sb-ext,
From:       "Nikodemus Siivola" <nikodemus () random-state ! net>
Date:       2008-03-13 21:14:25
Message-ID: 633d72b0803131414t5d57b162w30ce93820eba23a1 () mail ! gmail ! com
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On 3/13/08, Alexey Dejneka <adejneka@tochka.ru> wrote:

> How does it interact with INSERT-DEBUG-CATCH? What about
>
>  (locally (declare (optimize debug))
>   (defun foo (x)
>     (if (check x)
>         (surely-not-tail-call x)
>         (locally
>             (declare (optimize merge-tail-calls))
>           (tail-call-p x)))))

Neither ends up as a tail-call under my mental model. Practically
speaking, if one wants the semantic guarantee to have a reasonable
meaning the declare has to be in the outermost lexical scope.

My thought was mostly to make it possible to write

 (defmacro define-tco-fun (name lambda-list &body body)
   `(locally (optimize merge-tail-calls)
      (defun ,name ,lambda-list ,@body)))

in which case the MERGE-TAIL-CALLS declaration would trump things like
INSERT-DEBUG-CATCH.

Cheers,

 -- Nikodemus

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