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Re: Opaque syntax objects



On Sat, 13 Aug 2005, [ISO-8859-1] Jens Axel Søgaard wrote:

Representing syntax-objects using normal lists does breaks the
abstraction, and I too prefer the extra layer of abstraction.

This is often said, but I've never understood why people would think this. Normally subtyping (see my earlier message) or genericity are regarded as abstraction mechanisms, not abstraction-breaking mechanisms. After all, people don't normally say that generic + and * break the "integer" abstraction. Why should generic car/cdr be different here?

Keeping this abstraction doesn't make destructuring significantly more
impractical. Destructuring arguments using the pattern matching
capabilities of syntax-case is unchanged with both representations,


I feel strongly that pattern matching should be library syntax. For this proposal, I personally prefer a design based on a small procedural core + [quasi]syntax, rather than a rather complex special form.

and
in the case were it is neccessary to use normal Scheme operators, most
often a call to syntax->list, which turns a syntax-object representing a
list into a list of syntax-objects, is enough to solve the problem.

This can entail a rather expensive performance hit.

Cheers
Andre