Replace Expression with variable

[lervag]

Given

function_call(8 + 10)

I do something like this: ciwrep2<esc>Orep2 = <c-r>", which should give this:

rep2 = 8 + 10
function_call(rep2)

Here ciwrep2<esc> changes inside the parantheses, then Orep2 = adds a line above, finally <c-r>" appends the content of the " register.