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Re: (progn (top-level) A B C)


From: Andreas Schwab
Subject: Re: (progn (top-level) A B C)
Date: Wed, 14 Feb 2007 18:48:38 +0100
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/22.0.91 (gnu/linux)

A Soare <address@hidden> writes:

> Thanks, I will check. Another method that I found is
>
> (unwind-protect
>     (prog1
>         (message "x")
>       (top-level))
>   (message "a")
>   (message "b"))
>
>
> By the way, this code returns "Back to top level." . BAD.

It does not return anything.

> x
> a
> b
> Back to top level.
>
> What is the definition of prog1? It should return the first argument. It 
> seems that in this case the 1st argument is lost.

This is not a bug. (top-level) throws to 'top-level, thus (prog1 ...) is
never finished.  unwind-protect only returns a value if the body completes
normally.  Otherwise it does not return anything, rather execution is
transferred directly to the receiving exception handler after executing
the unwind forms.

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."




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