bash - Shell script to skip PPA if installed

I would like to create a script that will add a new PPA or skip if already installed.

Someone posted this solution to a different question:

#!/bin/bash 

add_ppa() {
      for i in "$@"; do
        grep -h "^deb.*$i" /etc/apt/sources.list.d/* > /dev/null 2>&1

        if [ $? -ne 0 ]
        then
          echo "Adding ppa:$i"
          sudo add-apt-repository -y ppa:$i
        else
          echo "ppa:$i already exists"
        fi
      done
    }

shell script to conditionally add apt repository

In my case I would like to add ppa:otto-kesselgulasch/gimp-edge, but I am not sure where I am supposed to add this in the script.

I tried add_ppa(ppa:otto-kesselgulasch/gimp-edge) but I keep getting an error saying (ppa is the name of my script):

ppa: 1: ppa: Syntax error: word unexpected (expecting ")")

I also tried with a space in between ppa and without the ()

ppa: 1: ppa: add_ppa: not found
ppa: 12: ppa: Syntax error: "}" unexpected

Can anyone tell me what am I doing wrong please?