is_latest() {
    exe="$1"
    latest="$2"
    installed="$3"
    silent="$4"
    if ! command -v "$exe" > /dev/null; then
        diag "$exe not installed; $latest available"
        return 1
    elif [ "$latest" = "$installed" ]; then
        test "$silent" = "silent" || diag "$exe already up to date"
    elif [ "$latest" = "" ]; then
        diag "[warn] 'latest' $exe is empty string"
    else
        diag "$exe $installed installed, but $latest available"
        return 1
    fi
}