Concatenating markup fragments in a function

[Andrew Bernard]

Sometimes in my scores I need to indicate a note name, with accidental, 
for example for very very high notes, just to aid the player. Sometimes 
I use a list to help out with very densely packed chords. [Don't blame 
me for this practice - it's my composer colleague!]

I am perfectly well aware I can user a markup such as "C#" with unicode 
accidentals. Fine. But I find the accidentals to be too small to read 
easily in my contexts, and the point of this is to enhance readability, 
so I have a function which uses a separate concatenation of an 
accidental so I can make the size larger. This works well.

\version "2.19.83"

#(define-markup-command (note-names layout props note-name accidental)
   (markup? markup?)
   "Provide note name for clarity."
   (interpret-markup layout props
     #{
       \markup {
         \override #'(font-name . "Latin Modern Sans Demi Cond")
         \concat
         {
           \fontsize #-1 \vcenter #note-name \hspace #.2
           \fontsize #-4 #accidental
         }
       }
     #}))


example:

  c'4
  ^\markup \note-names "C" \natural

[Using this function also gives me the possibilty to adapt it easily to 
use smufl accidentals which is something I also need, so there re 
multiple reasons for having this.]

But having made this function a while ago, I am going through some old 
scores which have lists of note names, like this:

_\markup \note-names "[A♯ B♮ C♯ D♯ F♯ G♯]"

Now what I would like to do is modify this to be able to say, in the 
same vein as the single name function above, for example:

 <c' e' gis'>
  ^\markup \note-names-multiple #'(("C" . \natural) ("E" . \natural) 
("G" . \sharp))


Here is my (very poor) sketch of what I need:

\version "2.19.83"

#(define-markup-command (note-names-multiple layout props note-names-list)
   (list?)
   "Provide multiple note names for clarity."
   (let ((txt ""))
     (let loop ((l note-names-list))
       (if (not (null? l))
           (begin
            (display (car l))
            (newline)
            (set! txt (string-append txt (car (car l))))
            (set! txt (string-append txt " "))
            (display txt) (newline)
            (loop (cdr l))
            )
           ))
     (interpret-markup layout props
       (markup txt)
       )
     ))

Obviously this is not complete. But I have come to a dead halt not 
knowing how I can glue bits of markup, rather than text, together inside 
the let loop, as per the single shot in the first function.

[Pardon me if this attempt looks like complete nonsense - I banged my 
head badly with much blood on the bandsaw in my workshop today and I 
confess I may not be thinking straight! Dear me.]


Andrew