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Re: Scheme Digest #125
For the sake of portability, I would like to plead with anyone who is
inventing a syntax for random values as part of a new Scheme system to use
the #! syntactic convention instead of grabbing yet another #X syntax,
where X is a character. For example, I plead with you to say #!unspecified
instead of #unspecified.
1. #!unspecified is already supported by several implementations.
More generally, there is a tradition of using similar #! syntaxes
for miscellaneous constants.
2. Within the Lisp world, most #X syntaxes are traditionally reserved
for user-defined extensions to the syntax accepted by the read
procedure. The syntax of Scheme reflects this tradition, in which
the first character following the # indicates the nature of the
syntactic extension. Note that there are only 26 (or 52) possible
#X syntaxes where X is a letter, and that Scheme has already
taken 8 (or 16) of these: #t, #f, #e, #i, #b, #o, #d, and #x.
This causes no problem for Scheme systems that don't support
user-defined #X syntaxes, but the existence of systems that do
support user-defined #X syntaxes makes it less likely that syntaxes
like #unspecified will ever become standard.