You can see from the rules in figure 3 that the sensory predicates are used on the left-hand side, as conditions. What about the right-hand sides?
The simplest thing the bug can do is to issue one of the eight primitive actions described in Introduction to Eden. If a rule wants to generate one of these actions, its right-hand side should look like this:
exec( [use] )or
exec( [forward] )
As well as the primitive actions, there are also some motor
competances. These are little chunks of program which combine the
primitive actions so as to do useful things. psbug1 uses only one
of these: it is
move_towards(+)This causes the bug to move a bit nearer a piece of food. If it is facing it, it will move one square in the appropriate direction; otherwise it will turn towards it.