barré variables and TextSpanner

[Federico Bruni]

I'm currently using these simple variables to reduce the clutter in my 
files:

barreI = \override TextSpanner #'(bound-details left text) = #"B I "
barreII = \override TextSpanner #'(bound-details left text) = #"B II "
barreIII = \override TextSpanner #'(bound-details left text) = #"B III "
...

I'm ok with adding \startTextSpan and \stopTextSpan every time. I just 
wanted to save some space in the music input.

Now I'd like to avoid this long list of frets and define a function 
which can take the fret as argument. So I can use:

\barre #"I"
\barre #"V"

I think that it would be easier to maintain, but I don't know where to 
start.
I've found this snippet in the LSR:
http://lsr.dsi.unimi.it/LSR/Item?id=632

But it's aimed at chords. Also, it works only in 2.14.2, not in 2.16

Thanks
--
Federico