Karel - introduction

Do you know robot Karel? It was created by Richard E. Pattis at Stanford University to teach basic programming skills. Karel was named after Karel Čapek, a Czech writer who introduced the word robot. (from Wikipedia).

Other information see on Wikipedia on (or Czech Wikipedie) or google. Note Google Translator can translate web pages to reading. Karel was very popular in Czechoslovakia on 8-bit computers. Most of programmers began their playing with Karel and QBasic. This pages deal about this version. Other informations on internet.

Robot Karel lives in his Town. The Town is a square (generally a rectangle) of squared fields in which wall or signs can be placed. There are walls around the Town also.

Karel has some basic skills.

• He can execute atomic commands:
  • STEP Karel moves to next square according his direction
  • LEFT Karel turns left
  • RIGHT Karel turns right (in some implementations must be defined by LEFT)
  • PUT Karel puts a sign under himself (if field is not full)
  • PICK Karel picks a sign from his field (if some sign is there.)
  • STOP Karel stops executing
• He can identify in which direction is turned
  • NORTH
  • EAST
  • SOUTH
  • WEST
  • (in some implementations only NORTH)
• He can recognize if there is a wall in his direction
• He can recognize if there is some sign under him
• He is angry if he crashes into the wall
• He is angry if he can't to pick or put a sign
• He can define new commands by construction
  

        DEFINE newcommand AS  
           commands  
        END 
    

  commands can be block of atomic commands or structural commands or previously defined commands. Structural commands are branching, while cycle and repeat cycle .
  
• branching :
  

        IF condition  
           commands  
        ELSE  
           commands  
        END  
        

  where ELSE part is not mandatory
  
• while cycle:

      
      WHILE condition  
          commands  
      END  
      

• repeat cycle:

      REPEAT # TIMES  
         commands  
      END 
      

  where condition can be
  IS WALL, NOT WALL,
  IS SIGN, NOT SIGN,
  IS NORTH, NOT NORTH , IS EAST, NOT EAST , IS SOUTH, NOT SOUTH, IS WEST, NOT WEST
  

A questions:

• Can be usefull atomic commands SLOWER and QUICKER to change speed (delay time)? E.g. to make shorter executing of command RIGHT using 3x LEFT to the user.
  Some implementations have it.
• If bad state of Karel (crash onto a wall, not able to pick or put, parsing errors) have to be thrown as Exception or returned as parameter?
  Running script executes in its own thread and it can be problem. E.g.