[plt-scheme] quasiquote?

From: Dor Kleiman (dor at ntr.co.il)
Date: Tue Jan 13 09:34:54 EST 2004

 From Revised^5 Report on the Algorithmic Language Scheme:
"If a comma appears followed immediately by an at-sign (@), then the
following expression must evaluate to a list"
A list, I believe, always refers to a proper list - otherwise it's not a
list, it's just a pair. Therefore, when using `(1 ,@(2 . 3)) it should
not work, but should raise an error.


-----Original Message-----
From: Joe Marshall [mailto:jrm at ccs.neu.edu] 
Sent: Tuesday, January 13, 2004 4:16 PM
To: Doug Orleans
Cc: plt-scheme at list.cs.brown.edu
Subject: Re: [plt-scheme] quasiquote?

  For list-related administrative tasks:

Doug Orleans <dougo at place.org> writes:

>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> Ken Anderson writes:
>  > I now see that args must be a list, which i assume means a proper
>  > 
>  > At 11:37 AM 1/7/2004 -0500, Ken Anderson wrote:
>  > >> (define name 'sscanf)
>  > >> (define args '(string format-string . args))
>  > >> `(,name . ,args)
>  > >(sscanf string format-string . args)
>  > >> `(,name , at args)
>  > >. append: expects argument of type <proper list>; given (string
format-string . args)
>  > >>
>  > >
>  > >>From my experience with Common Lisp i expected the two quasiquote
expressions to print the same.   Am i doing somethine wrong in Scheme or
is this a bug?
>  > >I'm using  200alpha12 (iteration 0)
> Coincidentally, I just ran into the same limitation: unquote-splicing
> only works on proper lists.  (Actually the one I ran into was
> unsyntax-splicing.)  R5RS only says its argument "must evaluate to a
> list", but it doesn't say proper list-- or is this always implied by
> the spec?  Anyway, is there a good reason not to extend it to work on
> improper lists as well?

I'd call it a bug.  

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