anchor.diff:  OR : 'or' ;
   LBRACE : '{' ;
   RBRACE : '}' ;
  +LBRACKET : '[';
  +RBRACKET : ']';
  +ARROW: '->' ;
   
   BooleanLiteral
      : 'true' | 'false'
  
positive.code: 
  grammar Lasca;
  
  valDef: VAL Id (':' type)? '=' expr;
  
  literal:
        IntegerLiteral # integer
  
negative.code: 
  blockStat
     : valDef
     | expr
     |
     ;
  