> 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 <co...@mercury.ccil.org> wrote:
> Its meaning is specifically left up to the implementation.  Apostrophe
> is neither a <subsequent> (required to be treated as part of the
> identifier) nor a <delimiter> (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.

> <http://trac.sacrideo.us/wg/wiki/QuoteDelimiter> 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 
(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

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 

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 
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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