Evaluate an expression in any mode
From Vim Tips Wiki
created August 3, 2003 · complexity basic · author Yakov Lerner · version 6.0
The <CTRL-R>= things evaluates the expression. For example:
<CTRL-R>= works in insert mode and in command mode. I felt it more convenient if <CTRL-R>= did the same thing in normal mode too.
I have this in my vimrc:
map <CTRL-R>= :echo
Now <CTRL-R>=123*456<CR> evaluates expressions for me in all 3 modes: normal mode, insert mode, and command mode. In fact I found it much more convenient to do casual calculations using <CTRl-R>= in normal mode than in any other mode.
Be warned: when typing <CTRL-R>= in normal mode, don't make long pause before '='. <CTRL-R> alone means 'redo' in normal mode. Vim is very smart, and figures the difference between single <CTRL-R> (which is 'redo') and the mapped sequence <CTRL-R>= (which is remapped). The 'timeoutlen' option controls this difference. The default value of 'timeoutlen' option is very convenient.
This is an expansion of Using Vim as calculator.
To get the behavior like i_CTRL-r in normal mode, use @=. For example, in normal mode, @='dd'<CR> will delete the current line just as if you had pressed dd in normal mode.
For more information. You can also do things like
:let @a = 'dd'
and then press @a in normal mode. This does the same thing.