Storing Ruby expressions to execute later

Is there a way to store rb expression so that can be interpreted
later. For example, i store as a string for example in my db "3+2" and
then at a later time i would like to execute it at future time. I am
allowing my users to generate code to analyze data and would like to
be able to allow the users to generate whatever expressions they see
fit. the actual expressino will be more complex but that is just an
example.

thanks,
tashfeen

Can you trust your users? Can you be confident they won't put
"User.delete_all" as Ruby code?