I see that the documentation for Racket's `read` and `read-syntax`
needs to be adjusted to say that the values of various parameters are
relevant only when the `read` or `read-syntax` starts. (Trying to make
them adapt dynamically in general would be impractical, I think; a
custom port's byte-reading callback could adjust a parameter's value on
every byte, and it would be difficult to specify the effect of those
changes.)
Without modifying the reader, I think you'd have to adjust the
readtable for everything that potentially starts a symbol, and then
parameterize a recursive read in those cases. That approach might not
be too bad, since a readtable supports a mapping for the fall-through
case, but I haven't tried it.
At Mon, 2 Nov 2015 15:34:33 -0800, Alexis King wrote:
> Hi all,
>
> I’m continuing to implement R7RS in Racket, and I think I’ve gotten most of
> the way aside from the various reader differences. The trickiest thing seems
> to be the #!fold-case and #!no-fold-case directives, which adjust the
> case-sensitivity of the reader as a side-effect. I’ve implemented a readtable
> dispatch macro on the exclamation mark, and I’ve been able to successfully
> read these two directives.
>
> Unfortunately, when I mutate read-case-sensitive by calling
> (read-case-sensitive #f) from within my readtable action, it doesn’t seem to
> persist this change to the next datum. However, the parameter is definitely
> getting set, because I get this error message:
>
>#!fold-case
>DISPLAY
>
>=> DISPLAY: unbound identifier in module in: |DISPLAY|
>
> The identifier in the error message is being escaped with |vertical bars|, as
> would be the case if case sensitivity were turned off. Unfortunately, it
> doesn’t seem to be affecting the symbols that actually get read.
>
> What’s the “proper” way to adjust this parameter dynamically as I read the
> program?
>
> Thanks,
> Alexis
>
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