Bill's vocabulary can be extended to include new words. However, these words are constructed from the set of primitive words. For example, a turnright instruction can be introduced as a set of three turnleft instructions. Because the turnright instruction comprises multiple primitive turnleft instructions, it must be defined as a block of turnleft instructions. The following is a sample structure of a program:
BEGINNING-OF-PROGRAM
DEFINE-NEW-INSTRUCTION turnright AS
BEGIN
turnleft;
turnleft;
turnleft;
END
BEGINNING-OF-EXECUTION
move;
turnleft;
move;
turnright;
pickbeeper;
turnoff;
END-OF-EXECUTION
END-OF-PROGRAM