vimrc syntax can't be vim recognized

[clay-f]

    function! InitializeDirectories()
        let parent = $HOME
        let prefix = 'vim'
        let dir_list = {
                    \ 'backup': 'backupdir',
                    \ 'views': 'viewdir',
                    \ 'swap': 'directory' }

        if has('persistent_undo')
            let dir_list['undo'] = 'undodir'
        endif

        " To specify a different directory in which to place the vimbackup,
        " vimviews, vimundo, and vimswap files/directories, add the following to
        " your .vimrc.before.local file:
        "   let g:spf13_consolidated_directory = <full path to desired directory>
        "   eg: let g:spf13_consolidated_directory = $HOME . '/.vim/'
        if exists('g:spf13_consolidated_directory')
            let common_dir = g:spf13_consolidated_directory . prefix
        else
            let common_dir = parent . '/.' . prefix
        endif

        for [dirname, settingname] in items(dir_list)
            let directory = common_dir . dirname . '/'
            if exists("*mkdir")
                if !isdirectory(directory)
                    call mkdir(directory)
                endif
            endif
            if !isdirectory(directory)
                echo "Warning: Unable to create backup directory: " . directory
                echo "Try: mkdir -p " . directory
            else
                let directory = substitute(directory, " ", "\\\\ ", "g")
                exec "set " . settingname . "=" . directory
            endif
        endfor
    endfunction
    call InitializeDirectories()

issue occur exec "set " . settingname . "=" . directory
vim version: 8.0