NOP is a dummy instruction that has no effect. It can be useful as the target of a THEN or ELSE clause.


  when a=c then nop           /* Do nothing */
  when a>c then say "A > C"
  otherwise     say "A < C"

Note: Putting an extra semicolon instead of the NOP would merely insert a null clause, which would be ignored. The second WHEN clause would be seen as the first instruction expected after the THEN, and would, therefore, be treated as a syntax error. NOP is a true instruction, however, and is, therefore, a valid target for the THEN clause.