anchor.diff:     : '<'
      ;
   
  +
   GTE
  -   : '>+'
  +   : '>='
      ;
   
   
   LTE
  -   : '<+'
  +   : '<='
      ;
   
   
  
positive.code:    ;
  
  ifblock
     : 'if' condition statement+ ('else' statement)? 'endif'
     ;
  
  whileblock
     : 'while' condition statement+
     ;
  
  doblock
     : 'do' statement+ 'while' condition
     ;
  
  assignblock
  
negative.code:    | GT
     | GTE
     | LT
     | LTE
     ;
  
  expressionlist
  