[R6RS] syntax-case semantics

[William D Clinger]

Kent wrote:
> I might buy the "hygiene issue" or whatever you want to call
> it if I had ever run into it or seen anyone else run into it,
> but I haven't.  So I prefer the traditional semantics.

I have run into the problem, so I prefer SRFI 72's semantics.

I also prefer SRFI 72's less opaque definition of a syntax object,
because it is less mysterious and because it allows the authors
of procedural macros to reuse more of Scheme's standard library
without having to mess with syntax-object->datum or syntax->list.

I also like SRFI 72's description of its semantics in terms of
a reflective tower.

I don't see much problem with the hash-table implementation of
source locations, because it should be easy to modify the macro
expander to record that information within fully macro-expanded
code in an implementation's preferred way, discarding the hash
table afterwards.  There is no need for weak pointers.

Will