Re: [Readable-discuss] treatment of quote symbol

[David A. Wheeler]

I said:
> > To be honest, I think we should treat x'x as an error in the sample
> > implementation (though guile treats x'x as a single symbol).  You can
> > always use |x'x| if you mean that, and if you mean (x 'x), we already
> > have several much clearer ways to express that:
> 

On Fri, 6 Dec 2013 10:58:25 -0500, John Cowan  wrote:
> +1

Okay, I've pushed that change, and it now reports more specifically what the 
problem is.
That means that x'y is no longer legal... and it will *immediately* identify 
that as an error
(and report the failing character, ' in this case).

This was never specified in SRFI-110 (or Scheme), so it's not a spec change...
it's just a way to more strict in a standards-compliant way.

--- David A. Wheeler

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Re: [Readable-discuss] treatment of quote symbol

[John Cowan]

David A. Wheeler scripsit:

> To be honest, I think we should treat x'x as an error in the sample
> implementation (though guile treats x'x as a single symbol).  You can
> always use |x'x| if you mean that, and if you mean (x 'x), we already
> have several much clearer ways to express that:

+1

-- 
Henry S. Thompson said, / "Syntactic, structural,   John Cowan
Value constraints we / Express on the fly." co...@ccil.org
Simon St. Laurent: "Your / Incomprehensible http://www.ccil.org/~cowan
Abracadabralike / schemas must die!"

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Re: [Readable-discuss] treatment of quote symbol

[Jörg F. Wittenberger]

Am 06.12.2013 07:01, schrieb David A. Wheeler:
> I'm guessing Joerg Wittenberger wants something else, though :-).
> So let's talk about that.
I just wanted to know whether the current behavior was an accident or 
intentional.

John's reply
http://trac.sacrideo.us/wg/wiki/QuoteDelimiter
made me aware that I overlooked a compatibility issue within Scheme itself.

So I'll eat the food (and insert spaces into my code where they are 
missing now).

/Jörg

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Re: [Readable-discuss] treatment of quote symbol

[David A. Wheeler]

> David A. Wheeler scripsit:
> > What do you think x'x *should* mean?  That's incredibly ugly!

On Thu, 5 Dec 2013 13:08:53 -0500, John Cowan  wrote:
> Its meaning is specifically left up to the implementation.  Apostrophe
> is neither a  (required to be treated as part of the
> identifier) nor a  (required to be treated as not part of
> the identifier).  Its general category is Po, which means that in R6RS
> and R7RS implementations are explicitly allowed to treat it as part of
> the identifier.

>  reports what Schemes
> actually do. Only a few of the major implementations actually allow
> x'x as an identifier.

SRFI-110 depends on other specs to define what symbols etc. are,
so formally SRFI-110 gives us a lot of freedom.

To be honest, I think we should treat x'x as an error in the sample 
implementation
(though guile treats x'x as a single symbol).  You can always use |x'x|
if you mean that, and if you mean (x 'x), we already have several
much clearer ways to express that:
(x 'x)
x('x)
x 'x

I'm guessing Joerg Wittenberger wants something else, though :-).
So let's talk about that.

It would probably be difficult to support x'x as 2 adjacent expressions
in many implementations in one special case: bare initial indents.
Since "read" must return, we depend on the unconsumed space or tab
to let us know that we're reading in the next item with an initial intend.
If we peek an apostrophe and don't consume it, there's no space or tab to 
inform.

It might be possible to support  x'x as 2 adjacent expressions in other cases,
though it might be awkward. Generally, if we consume an expression
and there's nonwhitespace left over, we complain about it,
as part of the general system to detect errors.
E.G., it-expr-real's complains about "Unexpected text after n-expression"
and we'd have to modify things to permit it.

It seems to me that x'x is almost certainly a mistake, and should cause an 
immediate
read failure as part of early error detection.  There are so few opportunities
for early error detection!!  Thoughts, anyone?

--- David A. Wheeler

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Re: [Readable-discuss] treatment of quote symbol

[John Cowan]

David A. Wheeler scripsit:

> What do you think x'x *should* mean?  That's incredibly ugly!

Its meaning is specifically left up to the implementation.  Apostrophe
is neither a  (required to be treated as part of the
identifier) nor a  (required to be treated as not part of
the identifier).  Its general category is Po, which means that in R6RS
and R7RS implementations are explicitly allowed to treat it as part of
the identifier.

 reports what Schemes
actually do.  Only a few of the major implementations actually allow
x'x as an identifier.

-- 
Only do what only you can do.   John Cowan 
  --Edsger W. Dijkstra's advice
to a student in search of a thesis

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Re: [Readable-discuss] treatment of quote symbol

[David A. Wheeler]

On Thu, 05 Dec 2013 13:14:34 +0100, "Jörg F. Wittenberger"  
 wrote:
> Hi all,
> 
> it's beginning to annoy me: normal Scheme readers treat quote and 
> quasiquote symbols as terminating charachters when reading symbols.
> 
> With the "readable reader" they suddenly become part of a symbol. That's 
> all rather confusing and causes so much incompatibility.
> 
> Its this really intended or just an oversight?

What do you think x'x *should* mean?  That's incredibly ugly!

--- David A. Wheeler

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