Structures

1
Structures

• Structures in LISP are analogous to that in C.
• To create a structure, use the following syntax
• (defstruct Name Slot1 Slot2 Slot3)
• An example would be
• (defstruct Submarine
• Course
• Speed
• Depth
• )

2
Creating instances

• To create an instance of the structure Submarine,
  do as follows
• (make-Submarine Course 90 Speed 5.5 Depth 200)
• This create and instance of Submarine and
  intializes the slots to the specified value.
• You could assign the instance to a variable
• (setq Sub1 (make-Submarine Course 90 Speed 5.5
  Depth 200))

3
Default values for slots

• You can also assign default values for the slots
  when you define the structure. For example,
• (defstruct Submarine
• (Course 180)
• (Speed 10.0)
• (Depth 250)
• )
• You can check the default values by
• (make-Submarine)

4
Accessing and setting slot value

• To access the slot value of an instance of a
  structure,
• (StructureName-SlotName InstanceName)
• To read the value of the slot Course of Sub1, do
  as follows
• (Submarine-Course Sub1)
• To set/modify the value of a slot, use the
  function setf
• For example, to set the slot Course of Sub1 to
  270, you could do this
• (setf (Submarine-Course Sub1) 270)

5
Type-of, typep

• If you have an instance of a particular
  structure, say for example Sub1, You could obtain
  the name of the structure by using the function
  type-of. For example,
• (type-of Sub1)
• typep is a predicate that tests for the type of
  aprticular structure instance. For example
• (typep Sub1 Submarine)
• The above expression will return t since Sub1 is
  an instance of Submarine.

6
Simple inheritance (1)

• Lets say that we wish to create another
  structure called Kilo, and we want it to inherit
  the definition of Submarine. This is can be done
  as follows
• (defstruct (Kilo (include Submarine))
• (SubType Assault)
• )
• This means that Kilo would inherit the slots
  defined by Submarine.
• It also adds another slot called SubType, and
  initializes it to Assault.

7
Simple inheritance (2)

• To create an instance of Kilo, you would do as
  so
• (setq Kilo1 (make-Kilo Speed 62))
• Then to access the value of Speed
• (Kilo-Speed Kilo1)
• (Submarine-Speed Kilo1)
• Testing for structure type
• (type-of Kilo1)
• (typep Kilo1 Kilo)
• (typep Kilo1 Submarine)