On Sat, 13 Aug 2005, [ISO-8859-1] Jens Axel Søgaard wrote:
Andre van Tonder wrote:
As we know, subtyping can be thought of in terms of implicit coercions.
The alternative is having explicit coercions as in PLT, the use of which
quickly becomes tedious when expressing simple things like
(apply append stx))
That particular example can be written very succintly with pattern matching:
Certainly. But consider instead something like
(apply lset-union literal-identifier=? syntax-list-of-syntax-lists)
where lset-union is from SRFI-1. Here you would be forced to do the
conversions as above.
Even worse, say we have an s-expression library with a procedure
(sexpr-map f x)
that applies f elementwise to non-pairs in x - maybe, to make it nontrivial,
efficiently avoiding cycles. In order to reuse sexpr-map to an opaque syntax
object, we would have no choice but to walk the whole object first to convert
it to an s-expression, basically defeating the purpose of using sexp-map in
the first place.
Cheers
Andre
