What is wrong with this mapping expression in my .vimrc?

Question

I'm trying to make Vim play nice with wrapped lines and I'm running into some problems. The following line

xnoremap <expr> k ((v:count == 0) || (mode() !=# "V") ? 'gk' : 'k')

gives me the following error when launching Vim

Error detected while processing /cygdrive/c/Users/Chad/.vimrc:
line   76:
E749: empty buffer

If I remove either of the conditions the map will work fine but I'd like to combine them. Any ideas? Thanks in advance.

Answer 1

See :h map_bar. The | is used also as a command separator in vim, so you are executing a map command:

xnoremap <expr> k ((v:count == 0) 

Then an empty command line, and after that a command:

(mode() !=# "V") ? 'gk' : 'k')

To use the | character in mappings, the two best options in my opinion are <Bar> or \|. Your mapping can be written as

xnoremap <expr> k ((v:count == 0) <Bar><Bar> (mode() !=# "V") ? 'gk' : 'k')

for example.