Re: Keyword syntax

[Roland Orre <orre@nada.kth.se>]

I like 1 more also. (I often use the non standard scheme way of
reading values with #something but I don't think that will
be a problem)

	Roland

On Mon, 2004-10-04 at 20:27, Marius Vollmer wrote:
> Hi,
> 
> I'm considering to change keywords are read or written by Guile, to
> make the two operations more consistent with each other.
> 
> Right now, keywords are read as a single token and a part of that
> token is made the keyword name, which is a symbol.
> 
> For example, a token can be "#:foo" (without the double quotes) and
> the name of the keyword is the symbol named "foo".  Also, "#:12" gives
> a keyword with a symbol as the name that itself has the name "12".
> Now, "12" is not a valid way to write this symbol in Scheme, and there
> for Guile writes the keyword #:12 in the following funny way:
> 
>     guile> #:12
>     #:#{12}#
> 
> The "#{12}#" is the syntax to write a symbol with an arbitrary name.
> 
> However, reading this printed form gives a different keyword.
> 
>     guile> #:#{12}#
>     #:#{\#{12}\#}#
> 
> 
> I can see two ways to fix this: 1) changing the way keywords are read and
> 2) changing the way they are printed.
> 
> As to 1), the simplest change would be to just do the equivalent of
> (symbol->keyword (read port)).  Thus, the name of a keyword is read as
> a general Scheme datum, and is then validated to be a symbol and
> converted to a keyword.
> 
> For 2), we would have to print keyword without using the symbol
> printer and would have to explicitely deal with 'weird' keyword names
> ourselves.
> 
> I have implemented 1) in CVS head as an experiment.  Below is a sample
> session, showing the differences.
> 
> I like 1) more than 2) (by a small margin) although it is a more
> radical change since keywords right now are defined to have symbols as
> names anyway and because it is equivalent to doing
> 
>     (read-hash-extend #\: 
>       (lambda (chr port)
>         (symbol->keyword (read port))))
> 
> which I like because it is very straightforward.
> 
> 
>     Previously
> 
>         guile> #:12
>         #:#{12}#
>         guile> #:#{12}#
>         #:#{\#{12}\#}#
>         guile> #:(a b c)
>         #:#{}#
>         ERROR: In expression (a b c):
>                Unbound variable: a
>         guile> #: foo
>         #:#{}#
>         ERROR: Unbound variable: foo
> 
>     With 1)
> 
>         guile> #:12
>         ERROR: Wrong type (expecting symbol): 12
>         guile> #:#{12}#
>         #:#{12}#
>         guile> #:(a b c)
>         ERROR: Wrong type (expecting symbol): (a b c)
>         guile> #: foo
>         #:foo
> 
> Opinions?
> 
> 
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