Question

I’m following Mapping keys in Vim – Tutorial (Part 1) – 6.2 Insert mode maps, and there it says:

The <C-R>= command doesn't create a new undo point.
You can also call Vim functions using the <C-R>= command:

:inoremap <F2> <C-R>=MyVimFunc()<CR>

I’m trying to use this to call SingleCompile#Compile() like:

map! <F5> <C-R>=SingleCompile#Compile()<CR>

It’s working, but the problem is that when I get back to insert mode, a 0 character is inserted as a side-effect.

Why is this and how can I avoid it?

EDIT:

I’m using <C-R> because it doesn’t create a undo point and has the purpose of calling a function instead of entering a command like <C-O> does. I don’t want to create a undo point.

EDIT:

I’ve updated the VIM wiki based on the ternary operator trick provided by Ingo Karkat.

Answer 1

The implicit return value of a function is 0. You need to either modify SingleCompile#Compile() or write a wrapper that returns the empty string:

function! SingleCompileWrapper()
    call SingleCompile#Compile()
    return ''
endfunction

map! <F5> <C-R>=SingleCompileWrapper()<CR>

An alternative clever trick is to evaluate the function inside the ?: ternary operator:

map! <F5> <C-R>=SingleCompile#Compile()?'':''<CR>