At one time or another, you will get caught in an infinite loop. Here are some particularly simple examples of programs which never terminate.
> do od;
> for i from 1 to 10 do
> if (i=10) then
> i:=1;
> fi;
> lprint('i = ', i);
> od;
To interrupt the computation, type the <control-c> sequence (press the c key while simultaneously holding down the control (or ctrl) key).