Some advocates of declarative languages suggest that logic programming should be used for all tasks. The idea is that one should be able to state WHAT the problem is and leave it to the computer to figure out HOW to solve it. Thus all one needs is assertions general facts, and questions, and not imperatives saying what to do when.
It is very natural, however, for people to think in terms of instructions as well as in terms of assertions and inference rules, and that is one reason why we have provided both in Poplog. For example, if someone asks you the way to the station, you will not usually succeed in communicating if you give lots of facts about where the station is located. Instead you will probably give some instructions:
go down that road until you come to the post office,
then turn left and.....etc
Of course, if the questioner knows the town very well, it may
suffice for him to be told:
the station is two blocks north of the post office.In order to make use of that information he will have to find some way of translating that into a plan for getting from where he is to the post office. The plan will contain a set of instructions about what to do when. Similarly, if you want the computer to do something other than tell you the answers to factual questions you often need to be able to give it instructions.
Even if all you are interested in is storing information and getting answers to questions relating to the information, someone must first tell the computer how to store information, and how to respond to questions. Thus instructions of some sort are required as the basis even for a purely declarative system.