Re: Issue 1428 in lilypond: \book cannot contain \bookpart identifier

[lilypond]

Comment #3 on issue 1428 by Carl.D.Sorensen: \book cannot contain \bookpart  
identifier
http://code.google.com/p/lilypond/issues/detail?id=1428

Here's a patch that eliminates the segfault -- it seems to be right to me,  
because it tests the part of $papers that will be used in the body of the  
if:


diff --git a/lily/lily-parser.cc b/lily/lily-parser.cc
index e0722fd..9a45fd9 100644
--- a/lily/lily-parser.cc
+++ b/lily/lily-parser.cc
@@ -270,7 +270,7 @@ push_paper (Lily_parser *parser, Output_def *paper)
 void
 pop_paper (Lily_parser *parser)
 {
-  if (! scm_is_null (parser->lexer_->lookup_identifier ("$papers")))
+  if (scm_is_pair (parser->lexer_->lookup_identifier ("$papers")))
     parser->lexer_->set_identifier (ly_symbol2scm ("$papers"),
                                     scm_cdr  
(parser->lexer_->lookup_identifier
 }