Re: Issue 1516 in lilypond: Crash with empty \markuplines

[lilypond]

Comment #1 on issue 1516 by address@hidden: Crash with empty  
\markuplines
http://code.google.com/p/lilypond/issues/detail?id=1516

\markuplines { } returns '(), which is valid according to markup-list? (and  
its C++
equivalent, Text_interface::is_markup_list ()):

foo = \markuplines { }

#(display (markup-list? foo))

-> #t

Assuming we want \markuplines { } to behave like \markup { } (i.e., produce  
a \null toplevel markup), then this patch works, since it ensures a valid  
Paper_score in paper-book.cc:

diff --git a/lily/parser.yy b/lily/parser.yy
index 0bb4c15..e6a7e09 100644
--- a/lily/parser.yy
+++ b/lily/parser.yy
@@ -2405,7 +2405,10 @@ full_markup_list:
        | MARKUPLINES
                { PARSER->lexer_->push_markup_state (); }
        markup_list {
-               $$ = $3;
+               if (scm_is_pair ($3))
+                       $$ = $3;
+               else
+                       $$ = scm_list_1 (scm_cons (ly_lily_module_constant  
("null-markup"), SCM_EOL));
                PARSER->lexer_->pop_state ();
        }
        ;

It's perhaps not the most elegant solution, so if anybody can come up with  
something better which doesn't cause any shift/reduce or reduce/reduce  
problems I'd be interested to see it. :)