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Re: The ". $" notation



Alan Manuel Gloria:
> >> 1.  Allow "foo . EOL INDENT x ..." ==> "(foo . (x ...))"
> >> 2.  Allow "foo . $ x ..." ==> "(foo x ...)"

Unfortunately, those 2 forms greatly differ in ease-of-implementation.

The *second* form is easy to add to the BNF.  Here's the patch:

diff --git a/sweet.g b/sweet.g
index 82055ea..937e54d 100644
--- a/sweet.g
+++ b/sweet.g
@@ -1061,6 +1061,7 @@ rest returns [Object v]
         (pn=n_expr hspace* (n_expr error)? {$v = $pn.v;}
          | COLLECTING hspace* pc=collecting_tail hspace*
            (n_expr error)? {$v = $pc.v;}
+         | SUBLIST hspace* ps=rest {$v = $ps.v;}
          | empty {$v = list(".");})
        | empty   {$v = list(".");})
   | scomment hspace* (sr=rest {$v = $sr.v;} | empty {$v = null;} )


So we could easily support form #2, and I don't see any big downside.
I'll post the ANTLR patch on git; we can revert it later, or implement it in the
Scheme implementation, depending on what people say.

I don't see an obvious way to add the first form to the BNF, though, and
I don't think we should reorganize everything for such a bizarre case.
Also, I can see form #1 being created accidentally, so *preventing* it seems wise.

Granted, that's a minor inconsistency, but ". $" is such a bizarre useless
sequence that I'm going to lose any sleep over it (if we add it).

--- David A. Wheeler