anchor.diff:      | LPAREN expression RPAREN
       ;
   
  +condition
  +    : term
  +    | (term (LT | GT | EQUALS) term)
  +    ;
  +
   comment
       : SEMICOLON ~(CR)*
       ;
  
positive.code:     ;
  
  for_
      : FOR SPACE+ term EQUALS term COLON term SPACE* (command SPACE?)* COLON (term (LT | GT) term)
      ;
  
  halt_
      : (HALT | 'H')
      ;
  
  hang_
  
negative.code:     ;
  
  set_
      : (SET) SPACE+ assign (',' assign)*
      ;
  
  assign
  