I'd earlier said:
> I'm looking for advice on how to implement, in Common Lisp, the
> sweet-expression semantics for {backquote,comma,comma-at}+whitespace.
Just to document my research...
Common Lisp can't unget multiple characters, but it does have the ability
"make-concatenated-stream". You can create a stream out of a string and park
that in front of another stream, resulting in a somewhat similar result:
http://www.lispworks.com/documentation/HyperSpec/Body/f_mk_con.htm
That lets me control what goes *into* read... but *not* the results that come
*out* of read. Sigh. The fundamental problem is that "read" has a fixed
interface, and I need read to *also* return any new indentation, if I want to
be able to use backquote with indentation-sensitive constructs. And I do.
So it looks like I'll have to re-implement backquote and comma in Common Lisp
if I want a portable thread-safe Common Lisp implementation. The good news is
that there is such an implementation:
> http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node367.html
On second glance it doesn't look *too* bad. Thankfully, this implementation
can be in its own file.
--- David A. Wheeler
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