如何正确使用强制转换而不需要括号?

How to correctly use coercions such that no parenthesis are needed?

为什么以下语法无法识别 nat -> nat 但可以识别 (nat -> nat),我该如何解决?

 TNat . Typ4 ::= "nat" ;                                                        
 TVoid . Typ4 ::= "<>" ;    
 TProd . Typ3 ::= SumType;                                
 TProd . Typ2 ::= Typ2 "*" Typ3;                                                
 TArrow . Typ1 ::= Typ1 "->" Typ2;                                              
 coercions Typ 4;      

颠倒声明顺序解决了问题

TArrow . Typ ::= Typ "->" Typ1;
TSum . Typ1 ::= SumType;
TProd . Typ2 ::= Typ2 "*" Typ3;
TNat . Typ3 ::= "nat" ;
TVoid . Typ3 ::= "<>" ;
coercions Typ 3;