[r6rs-discuss] Library naming ambiguity?

From: AndrevanTonder <andre>
Date: Tue, 12 Jun 2007 10:51:21 -0400 (EDT)

> This ambiguity can be removed either by:
>
> [1] Not allowing 'except' 'only' 'and' etc. as <identifier>s of
> the library.
>
> [2] By requring at least one <identifier> in except clause etc.

...and at least one <import level> in "for" clauses.

> The latter can certainly patch this specific problem, but I feel
> that the real problem is that the import syntax is too terse,
> conflating lists to carry too many meanings. It took some time
> for me to grok the import syntax described in 6.1.

I agree that it is hard to parse visually. It is also, in its
current form, very easy to code incorrectly.

> - Make 'only' etc. as qualifiers following <library-name>,
> instead of making them prefixed clause, e.g.
>
> (import (<identifier> <identifier>...) ; <library-name>, except <version>
> only <identifier> ...
> except <identifier> ...
> version <version-reference>)

I like this. This is much more readable, although this would need more
parentheses to be unambiguous, for example:

   (import (<identifier> <identifier>...) ; <library-name>, except <version>
           (only <identifier> ...)
           (except <identifier> ...)
           (version <version-reference>))

Apart from much better readability, a big reason I like your proposal more is
that it avoids proliferation of parentheses. The current syntax expresses
composing of import modifiers in prefix notation, which can lead to a
proliferation of parentheses. I particularly like your postfix notation
because it can express an arbitrary number of compositions in a constant
nesting level. I believe it will also be much easier to code a reliably
correct parser for it.

Andre
Received on Tue Jun 12 2007 - 10:51:21 UTC