David Kastrup <d...@gnu.org> writes:
>> Scheme has a very useful property which your proposed syntax would
>> destroy: any valid expression can be substituted for any other valid
>> expression, and the result has the same meaning except for the
>> substitution.
>
> guile> (display . (close (current-output-port)))
> #<primitive-procedure close>guile>
>
> Now try
>
> (define x (close (current-output-port)))
> (display . x)
Admittedly I could have been more clear, but I certainly didn't mean to
imply that anything that _looks_ like a valid expression can be
replaced. That would be absurd.
What I meant is that any _subexpression_ can be replaced with any other
valid expression, without changing the meaning of the program in any
other way. Whether something is a subexpression depends on its
_position_ within the larger expression.
In (display close (current-output-port)), even if you write it
confusingly in dotted-tail notation, (close (current-output-port)) is
_not_ a subexpression, because it is not in subexpression position.
The only advantage I see to this proposed syntax is that in some
restricted cases it is more aesthetically pleasing. I suspect that most
experienced Schemers have at some point wondered why dotted-tail
notation is not allowed in procedure calls. I certainly have, but upon
further consideration I became convinced that the pitfalls of adopting
such an ambiguous and potentially confusing syntax far outweigh the
advantages.
Thanks,
Mark
