Order of 'label-page-table

[Thomas Morley]

Hi,

I tried to define a markup-command which should allow to print some
markups in the page-header/footer depending on labeled pages.
It tooks me some time to identify, why it doesn't work as expected:
The 'label-page-table changes its order, if more than one label is on one page.

Heavily simplified example:

%%%%%%%%%%%%%%%%%%%%%%%%%%

\version "2.17.4"

#(define-markup-command (print-on-labeled-page layout props strg-label)
  (string?)
  (let* ((label (string->symbol (car (string-split strg-label #\_))))
         (arg (cadr (string-split strg-label #\_))))
    (ly:make-stencil
     `(delay-stencil-evaluation
       ,(delay (ly:stencil-expr
           (let* ((table (ly:output-def-lookup layout 'label-page-table)))

           (newline)(display "table ")(write table)     
           (interpret-markup layout props arg)))))
     '(0 . 9)
     '(0 . 2))))

%----- test --------

\paper {
        oddHeaderMarkup =
           \markup \fill-line {
                   \box \print-on-labeled-page #"a_Adagio"
                   \box \print-on-labeled-page #"b_Allegro"
                   \box \print-on-labeled-page #"c_Andante"
           }
        evenHeaderMarkup =
           \markup \fill-line {
                   \box \print-on-labeled-page #"a_Adagio"
                   \box \print-on-labeled-page #"b_Allegro"
                   \box \print-on-labeled-page #"c_Andante"
           }
}

\relative c' {
        \label #'a
        \repeat unfold 6 { c1 \break }
        \bar "|."
        \pageBreak %<===================
}

\relative c' {
        \label #'b
        \repeat unfold 6 { d1 \break }
        \bar "|."
}

\relative c' {
        \label #'c
        \repeat unfold 6 { e1 \break }
        \bar "|."
}

%%%%%%%%%%%%%%%%%%%%%%%%%%

With the pageBreak the terminal returns:
table: ((b . 2) (c . 2) (a . 1))
I.e. the list-elements-cars doesn't match with the occurrence of the
labels, nor the reversed list.

Without pageBreak:
table: ((a . 1) (b . 1) (c . 1))


Well, I managed to order the list with some scheme-code:

%%%%%%%%%%%%%%%%%%%%%%%%%%

#(define l '((f . 4)(g . 4)(d . 3)(e . 3)(c . 2) (a . 1) (b . 1)))

#(define (split-at-equal-cdr alist)
"After `split-at-predicate´ from lily-library.scm
 BTW, why is it not public?
"
  (if (null? alist)
    (list alist)
    (let ((i (list-index
               (lambda (x y) (not (= (cdr x) (cdr y))))
                 alist
                 (cdr alist))))
       (if i
           (cons (take alist (1+ i)) (drop alist (1+ i)))
           (list alist)))))

#(define (order-alist l)
    (define (helper l1 l2)
        (if (null? l1)
          l2
          (helper
            (cdr (split-at-equal-cdr l1))
            (append (car (split-at-equal-cdr l1)) l2))))
  (helper l '()))

#(write (order-alist l))

%%%%%%%%%%%%%%%%%%%%%%%%%%

Returns: ((a . 1) (b . 1) (c . 2) (d . 3) (e . 3) (f . 4) (g . 4))
and would be ok.



Is there any reason for the default-behaviour of 'label-page-table?
If not, could it be changed easily?
Or must I postprocess the 'label-page-table with my `order-alist´?

I found
  // By reversing the table, we ensure that duplicated labels (eg. those
  // straddling a page turn) will appear in the table with their last
  // occurence first.
in page-breaking.cc, but because of my lack of C++ - knowledge, I
can't read, understand or appraise the coding.


-Harm