Cycle between keyword & user defined completion with C-N

Question

I use the following mapping to initiate keyword completion, followed by user defined completion:

inoremap <expr> <c-n> pumvisible() ? "\<c-x>\<c-o>" : "\<c-n>"

How can I rewrite this mapping so that repeatedly pressing <c-n> results in the cycling of keyword and user defined completion?

Answer 1

I'm not sure when exactly you would initiate the cycling (as you typically use <C-N> to both trigger and go through the list of matches), but the key to implementing this is via a boolean flag stored in a variable. To be able to use :let to toggle this, you need to move from an inline expression to a function (which still returns the chosen completion key).

inoremap <expr> <c-n> TriggerOrToggleCompletion()
function! TriggerOrToggleCompletion()
    ...
endfunction