number syntax

[Jonathan A Rees <JAR@MIT-AI.ARPA>]

    Date: Tue 17 Jun 86 16:00:31-CDT
    From: David Bartley <Bartley%ti-csl.csnet at CSNET-RELAY.ARPA>
    To:   RRRS-Authors%mit-mc at CSNET-RELAY.ARPA
    cc:   Bartley%ti-csl.csnet at CSNET-RELAY.ARPA
    Re:   Number syntax
    Message-Id: <12215615581.31.BARTLEY@CSC60>
    
    One irritant in the Report that we have neglected to comment on until
    now (sorry!) is the syntax of numbers.  We believe that Scheme numbers
    are essentially equivalent to Common Lisp numbers except for the new
    notion of exactness.  To the extent that that is so, it seems to be a
    (shudder!) ``gratuitous difference'' from Common Lisp to have an
    incompatible syntax.
    
    The R^3RS doesn't make clear which subset of the syntax of numbers is
    essential and what is optional.  As implementors of systems in which
    Scheme and Common Lisp must co-exist, we're faced with two potential
    compatibility issues: (1) going with an ``extended subset'' of the
    Report's number syntax that is compatible with Common Lisp, or (2)
    going with the full number syntax in the Report to be compatible with
    all other Scheme implementations.
    
    What we'd like to see is an essential syntax for numbers which is
    compatible with Common Lisp's.  Additional features, including
    exactness, would be optional extensions.  Even so, they should not
    conflict with Common Lisp.  For example, the use of `#s' and the order
    of <sign> and <prefix> are different in the two languages.
    
    Our motivation, of course, is that we'd like programmers to feel free to
    use either language and exchange files of data without irritating
    obstacles being thrown in their path.  If we can't agree on a
    consistent syntax for numbers, then we'll have to provide each language
    with two readers and the user will have to know which one to use.
    
    (There are other problems, of course, such as whether `:' is a
    constituent of an identifier or associated with Common Lisp package
    designations.  We may have to go with separate readers/modes anyway.)
    
    Does anyone agree with us?  Is there time to make such a change before
    R^3RS goes to press?

I think everyone agrees with you, and that there is time.  Could you
please write a concrete proposal, preferably something close to being
suitable for inclusion in the report.  Also please provide BNF.  Thanks.

Jonathan