Add Scheme function to return column associated with Item. (issue 203910043 by address@hidden)

[david . nalesnik]

Reviewers: ,

Message:
Please review.

Description:
Add Scheme function to return column associated with Item.

The C++ function PaperColumn::get_column is used frequently,
and it makes sense to have a Scheme function which performs
the same task.  An example of a practical application
is the request by users to return the location of a particular
grob in a score: this is done by examining the PaperColumn
or NonMusicalPaperColumn associated with the grob.

Please review this at https://codereview.appspot.com/203910043/

Affected files (+15, -0 lines):
  M lily/item-scheme.cc


Index: lily/item-scheme.cc
diff --git a/lily/item-scheme.cc b/lily/item-scheme.cc
index  
0e6b71ef30a8191931495c3ff16bd6d9bb5fcadb..24ccf5bf0de97ba6666751afa514b2e777392c73  
100644
--- a/lily/item-scheme.cc
+++ b/lily/item-scheme.cc
@@ -19,6 +19,7 @@
 */

 #include "item.hh"
+#include "paper-column.hh"

 LY_DEFINE (ly_item_p, "ly:item?",
            1, 0, 0, (SCM g),
@@ -39,3 +40,17 @@ LY_DEFINE (ly_item_break_dir, "ly:item-break-dir",
   Item *me = Item::unsmob (it);
   return scm_from_int (me->break_status_dir ());
 }
+
+LY_DEFINE (ly_item_get_column, "ly:item-get-column",
+           1, 0, 0, (SCM it),
+           "Return the @code{PaperColumn} or @code{NonMusicalPaperColumn}"
+           " associated with this @code{Item}.")
+{
+  LY_ASSERT_SMOB (Item, it, 1);
+  Item *me = Item::unsmob (it);
+
+  if (Paper_column *col = me->get_column ())
+    return col->self_scm ();
+
+  return SCM_EOL;
+}