As far as I know, that is the sole function.

Its sole function is to centralize the management of a significant family fortune.

Officials did acknowledge the presence of the military police at the jail but said their sole function was to "monitor his treatment."

He had a hand-picked team whose sole function was to do just that.

But science does not contend that this is the sole function of humanity.

The sole function of a railroad was to make money for the insiders.

Wouldn't it be nice if each country had a governmental department whose sole function was to promote peace?

There were eight historiographers whose sole function was to record the meetings for history.

She has no known authority or decision-making control; instead her sole function is to reproduce.

Their sole function must have been to prevent one from getting lost in total blackness.