function help

[No Body]

Hello,
I'm trying to make a fingering function for use with tab that takes a string, such as "12345" or "23", breaks it apart and stacks it in a column with a circle around each number.  I've commented out part of my feeble attempt at a function so that my desired result can be produced with only markup. I've read and read and am at the end of my wits. Any help would be greatly appreciated! Thanks, Robby

Here's my code:

\version "2.18.2"

% ****** Parts of this are commented out
fing = #(define-scheme-function
     (parser location str) (string?)
    
     ( markup
         ;#:column
         ;(map (lambda (c) ( #:circle (string c) ))(string->list str))
     )
)

% ****** fingering markup
fingAll = \markup {
  \column {
    \circle 5
    \circle 4
    \circle 3
    \circle 2
    \circle 1
  }
}

music = {
    \relative c' {
        \displayMusic { b4\2^\fingAll a\3 c\2^\fing "678"   g\2 }
    }
}

\score {
  <<
    \new TabStaff {
          \tabFullNotation
    \set TabStaff.stringTunings = #banjo-open-g-tuning
    \music
    }
  >>
}