I think I've improved special comment handling.
The previous BNF could handle special "comment" markers like "#!sweet", but you
couldn't have blank lines after them.
The reason was that once we see "#", we need to invoke the it-expression
machinery to process it, because "#" can introduce all sorts of constructs
(vectors with #(), etc.). But once we invoke it-expression processing, the
it-expression machinery has to produce *something*. That production doesn't
really have a "produce nothing" case. Our current Scheme implementation uses
special cons cells to indicate things like this, but it'd be much cleaner if we
didn't need those kinds of hacks.
I think instead we should modify the it_expr production so that if it sees
"#!sweet" etc. all by itself on a line, it just keeps reading empty lines until
it finds something. That way, we don't have a special case... it_expr
eventually finds something to return. My approach disables initial-indentation
processing for the next expression, but I don't think that's a problem.
This means that in i_expr, in the case of:
| (GROUP_SPLICE | scomment) hspace* /* Initial; Interpet as group */
(group_i=it_expr {$v = $group_i.v;} /* Ignore initial GROUP/scomment */
| comment_eol
(indent g_body=body {$v = $g_body.v;} /* Normal GROUP use */
....
We just change:
| same g_i=it_expr {$v = $g_i.v;} /* Plausible separator */
into this, adding "(comment_eol same)*" :
| same (comment_eol same)* g_i=it_expr {$v = $g_i.v;}
That should make sweet-expressions easier to use.
A side effect is that an initial "\\" on a line, with nothing after it, will
consume blank lines that follow. But you can't use "\\" in the middle of an
expression to consume arbitrary blank lines; once you indent, a blank line
still generates dedents which end the expression. It would be very difficult
to do otherwise, as far as I can tell, without major surgery and the loss of
other capabilities (esp. ease-of-use at the UI). So this represents a small
tweak so that stuff like #!special-stuff can be handled, and not a significant
change in how sweet-expressions are used.
--- David A. Wheeler
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