The Spider Package

PACKAGE Spider IS|
----------------------------------------------------------------
--| This package provides procedures to emulate "Spider"
--| commands. The spider can move around
--| the screen drawing simple patterns.
--| Author: John Dalbey, Cal Poly San Luis Obispo, 1992
--| Adapted by M. B. Feldman, The George Washington University
--| Last Modified: December 1998
----------------------------------------------------------------

  -- These are the spider's simple parameterless method

  PROCEDURE Start;
  -- Pre:  None
  -- Post: Spider's room appears on the screen
  --   with spider in the center.

  PROCEDURE Quit;
  -- Pre:  None
  -- Post: End the drawing

  PROCEDURE Step;
  -- Pre:  None
  -- Post: Spider takes one step forward in the direction it is facing.
  -- Raises: Hit_the_Wall if spider tries to step into a wall.

  PROCEDURE TurnRight;
  -- Pre:  None
  -- Post: Spider turns 90 degrees to the right

  -- now some types, and methods that use the types

  TYPE Directions IS (North, East, South, West);
  TYPE Colors     IS (Red, Green, Blue, Black, None);
  SUBTYPE Steps IS Integer RANGE 1..20;

  PROCEDURE Face (WhichWay: IN Directions);
  -- Pre:  WhichWay has been assigned a value
  -- Post: Spider turns to face the given direction.

  FUNCTION IsFacing RETURN Directions;
  -- Pre:  None
  -- Post: Returns the direction the spider is facing.

  FUNCTION RandomDirection RETURN Directions;
  -- Pre:  None
  -- Post: Returns a random direction

  PROCEDURE ChangeColor (NewColor: Colors);
  -- Pre:  NewColor has been assigned a value
  -- Post: Spider leaves its tracks in the new color

  FUNCTION IsPainting RETURN Colors;
  -- Pre:  None
  -- Post: Returns the color in which the spider is painting

  FUNCTION RandomColor RETURN Colors;
  -- Pre:  None
  -- Post: Returns a random color

  FUNCTION AtWall RETURN Boolean;
  -- Pre:  None
  -- Post: Returns True if the spider is standing next to a wall

  FUNCTION RandomStep RETURN Steps;
  -- Pre:  None
  -- Post: Returns a random number in the range 1..20

  Hit_The_Wall: EXCEPTION;

  TYPE Switch IS (On, Off);

  PROCEDURE Debug (Setting: Switch);
  -- Pre:  None
  -- Post: Turns on or off single stepping through the program.

  FUNCTION  Debugging RETURN Switch;
  -- Pre:  None
  -- Post: Returns on or Off depending on Debug setting

END Spider;