Check nerd tree is open function

Question

I'm trying to create a simple function in vim which lets me map <leader>b, <leader>n, and <leader>0 to execute a function that checks if a nerd tree is open then cycle tabs and do :NerdTreeFind if not then only cycle tabs. but I couldn't seem to make it work and it returns E121: Undefined variable: CR

here is the script

function! CheckNerdTree(tab)
    if exists("g:NERDTree") && g:NERDTree.IsOpen()
        execute a:tab<CR>:NERDTreeFind<CR><C-w>l<CR>
    else
        execute a:tab<CR>
    endif
endfunction


noremap <leader>0 :call CheckNerdTree(":tablast")
noremap <leader>n :call CheckNerdTree(":tabnext")
noremap <leader>b :call CheckNerdTree(":tabprev")

I'm pretty new to vim scripting and haven't really 100% understand how it works, any help would be appreciated. Thanks

Answer 1

The execute command takes a string as an argument. Further, it is used to execute Ex commands. Finally, Ex-commands may be « executed » (in the programmatic sense, not the vimscript sense!) by simply calling them.

So we can simplify to

execute a:tab
NERDTreeFind
wincmd l

And

execute a:tab

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Don’t forget the <CR>s at the end of the mapping