# -*- mode: sh; -*-
if [[ ! "${(P)${1}}" =~ (^|:)"$2"(:|$) ]]; then
    if [ -n "$3" ]; then
        # Append
        typeset -g $1="${(P)${1}}:$2"
    else
        # Prepend
        typeset -g $1="$2:${(P)${1}}"
    fi
fi