Most scenarios in interactive fiction will not require a loop. But for completion and the possible situation where you might need a loop I have included it here. I used the Inform 7 syntax document to concoct these examples: http://inform7.com/learn/documents/I7_syntax.txt
The dog park is a room.
A stick is in the dog park.
After dropping stick:
repeat with index running from 1 to 10
There is syntax for a while loop, but I haven’t found a way to use it better than the use of an every turn rule ….
If player carries the one ring:
say “The ring is such a burden to bear!”.