Aaron W. Hsu scripsit:

> Let's keep in mind the text of the standard, which should match that of
> R6RS for this case, and therefore, we can test any Scheme implementation
> claiming to conform to R6RS to see if we get what we expect.

[snip]

> This gives '(a b c d a b) as the only valid result.

And indeed, that's what we get from Chez, Ikarus, Vicare, Larceny,
Ypsilon, Mosh, Chibi.  However, IronScheme, Racket (in #lang r6rs mode),
STklos all return (a b c d), for whatever reason.  SigScheme returns
(a c d b), though its definition of `guard` may be different.  My other
Schemes all report errors, typically about `guard` or `raise` being
undefined, or that `(#t #f)` is not a valid procedure call.

Thanks for writing a detailed explication.  I've added it to the ticket.

--
They do not preach                              John Cowan
  that their God will rouse them                cowan@ccil.org
    A little before the nuts work loose.        http://www.ccil.org/~cowan
They do not teach
  that His Pity allows them                         --Rudyard Kipling,
    to drop their job when they damn-well choose.   "The Sons of Martha"

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