variable variables

[Gerjan Piksen]

Hi everyone,

In the piece I’m writing right now I use a lot of clusters, to notate these 
clusters i use a custom note head. And the code looks like this:

qRecta=
#(ly:make-stencil (list 'embedded-ps
"gsave
currentpoint translate
newpath
0 0.55 moveto
0.33375 0.55 lineto
0.33375 -0.55 lineto
0 -0.55 lineto
closepath
fill
grestore")
  (cons 0.5 1.3125)
  (cons 0 0))

In my \score I can recall this with:

\override NoteHead #'X-offset = #0
\override NoteHead #'stencil = \qRecta

What I would like is to be able to change the length of my rectangle note 
heads. therefore i have to change this number 0.33375.
So what i would like is something like this:

qRecta=
#(ly:make-stencil (list 'embedded-ps
"gsave
currentpoint translate
newpath
0 0.55 moveto
X 0.55 lineto
X -0.55 lineto
0 -0.55 lineto
closepath
fill
grestore")
  (cons 0.5 1.3125)
  (cons 0 0))

\score 
{ \absolute
\override NoteHead #'X-offset = #0
\override NoteHead #'stencil = \qRecta
\X = 0.3 <e' f' g’ a’ b’ c’>8 \X = 0.5 <e' f' g’ a’ b’ c’>8
}

I would be very very very happy with some help on this : )