Even without resorting to external tools the expression register(:h @=) can act as a surprisingly good builtin calculator, and there is a moderately large builtin math library(:h functions).
Like all registers you can abuse it in many ways too, like as dirty inplace calculator when you're writing docs. For example, yank a example calculation, insert from register(:h i_CTRL-R_=), operate on your yank(:h @").
Like all registers you can abuse it in many ways too, like as dirty inplace calculator when you're writing docs. For example, yank a example calculation, insert from register(:h i_CTRL-R_=), operate on your yank(:h @").