HP 3000 Manuals

Understanding Your System Concept Guide for the HP 3000 Series 9X7LX

A Practical Problem 

If you were writing a program designed to put out a fire, you might write
something like this:

     program stopfire(telephone, first aid, water){what is needed}
     begin                             {start the program}
       call firemen                       {a simple command}
       get people out of the house        {a simple command}
       if someone is hurt then            {a single question}
         begin                              {start special action}
           call a doctor                      {a simple command}
           administer first aid               {a simple command}
         end                                {stop special action}
         look at the house                {a simple command}
         while the house is burning       {a continuing question}
           begin                            {start special action}
             pour on more water               {a simple command}
             look at the house                {a simple command}
           end                              {stop special action}
       end                             {stop the program}

The idea behind creating programs is no more complicated than this.
True, most computer programs are more complicated.  But the idea is the
same.

You might re-write the program to specify even more details about what to
do.

Here, begin and end are commands--not to perform a particular action, but
to show where particular actions (or groups of actions) start and stop.

Make note of while.  It introduces a question that will be asked not
once, but many times.  The begin and end that follow it surround
particular actions that will be performed over and over, until the house
is no longer burning.

The ability of programs to control repetitive actions such as these give
computers much of their power to solve problems.  Programs divide big
problems into small problems and speedily work at solving the small
problems until all of the little solutions add up to a big solution.

MPE/iX 5.0 Documentation