Auto_change_iterator: move some state from C++ to Scheme (issue 248470043 by address@hidden)

[nine . fierce . ballads]

Reviewers: ,

Description:
Auto_change_iterator: move some state from C++ to Scheme

This simplifies the iterator and prepares it for future combination
with partcomine code.

Please review this at https://codereview.appspot.com/248470043/

Affected files (+16, -21 lines):
  M lily/auto-change-iterator.cc
  M scm/autochange.scm


Index: lily/auto-change-iterator.cc
diff --git a/lily/auto-change-iterator.cc b/lily/auto-change-iterator.cc
index  
e72b53d9bed764c6338607dadb52382864ce1850..d295628326a32c47555ed6f5e23e7d95573c65b5  
100644
--- a/lily/auto-change-iterator.cc
+++ b/lily/auto-change-iterator.cc
@@ -38,7 +38,6 @@ protected:
   vector<Pitch> pending_pitch (Moment) const;
 private:
   SCM split_list_;
-  Direction where_dir_;

   Context_handle up_;
   Context_handle down_;
@@ -47,8 +46,6 @@ private:
 void
 Auto_change_iterator::process (Moment m)
 {
-  Music_wrapper_iterator::process (m);
-
   Moment *splitm = 0;

   for (; scm_is_pair (split_list_); split_list_ = scm_cdr (split_list_))
@@ -57,25 +54,18 @@ Auto_change_iterator::process (Moment m)
       if (*splitm > m)
         break;

-      SCM tag = scm_cdar (split_list_);
-      Direction d = to_dir (tag);
-
-      if (d && d != where_dir_)
-        {
-          where_dir_ = d;
-          string to_id = (d >= 0) ? "up" : "down";
-          // N.B. change_to() returns an error message. Silence is the  
legacy
-          // behavior here, but maybe that should be changed.
-          Change_iterator::change_to (*child_iter_,
-                                      ly_symbol2scm ("Staff"),
-                                      to_id);
-        }
+      // N.B. change_to() returns an error message. Silence is the legacy
+      // behavior here, but maybe that should be changed.
+      Change_iterator::change_to (*child_iter_,
+                                  ly_symbol2scm ("Staff"),
+                                  ly_scm2string (scm_cdar (split_list_)));
     }
+
+  Music_wrapper_iterator::process (m);
 }

 Auto_change_iterator::Auto_change_iterator ()
 {
-  where_dir_ = CENTER;
   split_list_ = SCM_EOL;
 }

Index: scm/autochange.scm
diff --git a/scm/autochange.scm b/scm/autochange.scm
index  
a6c78f7bbcff8249def1f65aac2257de9d6a3467..17358aebe038b17986e76b455f0d10f4c1b9bacb  
100644
--- a/scm/autochange.scm
+++ b/scm/autochange.scm
@@ -4,7 +4,7 @@
 ;; autochange.scm - fairly related to part combining.

 (define-public (make-autochange-music music)
-  (define (generate-split-list change-moment event-list acc)
+  (define (generate-split-list change-moment prev-dir event-list acc)
     (if (null? event-list)
         acc
         (let* ((now-tun (caar event-list))
@@ -15,19 +15,23 @@
                               evs))
                (pitch (if (pair? notes)
                           (ly:event-property (car notes) 'pitch)
-                          #f)))
+                          #f))
+               (dir (if pitch (sign (ly:pitch-steps pitch)) 0)))
           ;; tail recursive.
-          (if (and pitch (not (= (ly:pitch-steps pitch) 0)))
+          (if (and (not (= dir 0))
+                   (not (= dir prev-dir)))
               (generate-split-list #f
+                                   dir
                                    (cdr event-list)
                                    (cons (cons

                                           (if change-moment
                                               change-moment
                                               now)
-                                          (sign (ly:pitch-steps pitch)))  
acc))
+                                          (if (< dir 0) "down" "up")) acc))
               (generate-split-list
                (if pitch #f now)
+               dir
                (cdr event-list) acc)))))

   (let* ((m (make-music 'AutoChangeMusic))
@@ -38,6 +42,7 @@
          (rev (reverse! (cdar context-list)))
          (split (reverse! (generate-split-list
                            #f
+                           0
                            rev
                            '())
                           '())))