scheme function with string

[Gianmaria Lari]

I have this simple scheme substitution function

myFin = #(define-music-function (m)  (ly:music?)

    #{ \addStringNumber \addFingering $m "1x2x" "x3x4" #}

)

It simply adds some fingering and string numbers on the musical _expression_ argument m. I use like this: 

\myFin {a b c' d'}

I would like to modify "myFin" function adding two more string parameters so that I can pass the fingering strings. In the end I would like to be able to write 

\myFin {a b c' d' "1x2x" "x3x4" }

How can I do it?

Thank you, g.