Free42 / Plus42 - System or built-in keyboard on iOS / Android?

[Vincent Weber]

You can't.

Thomas has not coded the handler that would allow that.
It seems that it is low priority on his list, given the fact that all functions are available in menus and that you have many clever shortcuts for entering equations, so the need to type a function in full is quite reduced. Only for typing a long variable name maybe. But then you can create it once using the normal double-stroke entry, and then recall it from the equation editor for any subsequent occurrence.

Maybe someday...