On 8/22/12, David A. Wheeler <dwhee...@dwheeler.com> wrote:
> I said:
>> > Here's an alternative: Couldn't the sweet-expression reader peek for an
>> > initial "#", and if it's there, re-implement *just* # processing? Then
>> > it could include support for the "comment-tag" for #|...|#, but it'd be
>> > isolated to the sweet-expression level. That'd isolate it to just the
>> > sweet-expression processing. Then neoteric-read would only encounter
>> > #|...|# inside a list, where it could recurse without problems.
>
> Alan Manuel Gloria:
>> This sounds like a better idea. The sweet-expression reader already
>> does something different when it encounters # at the top-level.
>
> Okay, that's now implemented in the devel branch. Looks like it works well.
> So let's leave #|...|# semantics as they are. We'll need to do more code
> simplifications, since that is no longer needed in the lower tiers, and the
> sweet-expression implementation is still clunky, but that can be done in
> stages.
Wait, the implementation does not seem correct...
parse-hash is not assured of leaving the port in a decent state if it
returns #f; i.e. it could consume the character after the #. The
current Guile implementation behaves decently, but the comments at the
top of the file don't reflect that. I think it would be better to
copy even more of process-sharp's code rather than calling into
process-sharp, so that the standard Scheme syntaxes are considered
*before* calling parse-hash.
I suppose this is due to a desire to reduce the code size by not
rewriting process-sharp.
How about, making process-sharp-comment-tag the more "basic" function,
and having process-sharp be:
(define (process-sharp no-indent-read fake-port)
(let ((rv (process-sharp-comment-tag no-indent-read fake-port)))
(if (eq? rv comment-tag)
(no-indent-read fake-port)
rv)))
Of course, comment-tag still "infects" underlying read, but I think
that's acceptable...
Alternatively, make process-sharp return a *list*, i.e. use the same
calling convention for parse-hash. Then in the underlying-read, check
for '() and recurse if it is, or return the car if not. This
alternative removes comment-tag as well, and you can return
comment-tag into process-sharp-comment-tag by simply converting '() ->
comment-tag and (a) -> a
Sincerely,
AmkG
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