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