lilypond 2.21 & scheme unbound variable

[Gianmaria Lari]

The following function has been written by David Kastrup few years ago but it does  not compile on lilypond 2.21

\version "2.21.0"

newFinger =

#(define-event-function (arg) (number-or-markup?)

  #{ -\markup \underline \finger

     #(if (number? arg) (number->string arg) arg)

  #})

The error I get is the following:

error: GUILE signaled an error for the _expression_ beginning here

#

(define-event-function (arg) (number-or-markup?)

Unbound variable: number-or-markup?

Unbound variable: number-or-markup?

How can I fix it?

Thank you, g.