[R6RS] issues in document/lex.tex

William D Clinger will at ccs.neu.edu
Mon Aug 28 09:42:01 EDT 2006

Mike wrote:
> > Searching the R5RS, it appears to me that <datum>
> > always means an external representation, except for
> > some fairly harmless abuse of the term in the
> > descriptions of case expressions and the syntax of
> > lists.
> That's because R5RS punts on a precise description of the connection
> between datums and external representations.  In the place where it
> matters most, namely the description of `quote', the confusion is
> especially apparent.  Whether it's harmless is a matter of judgement,
> I guess, but I've sure always found it pretty serious, especially when
> showing it to people not already familiar with Lisp or Scheme lore.

In the R5RS, a <datum> *is* an external representation.
In the current draft of the R6RS, you have changed the
meaning of datum to mean an *object* that has an external
representation.  Not only is that a radical change in
terminology from the R5RS, it exacerbates the precise
confusion you are trying to avoid.

Another thing:  In English, the plural of "datum" is
"data", not "datums".  The non-word "datums" does not
appear within the R5RS, according to my quick search,
although "<datum>s" probably does.


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