语义分析的例子 w Type equivalence and compatibility w Two base types are equivalent if and only if they are the same exact type BoolEXpr ExprI$$= Check BoolExprUsage(&@1, $1); * Check BoolExprUsageo中检查$即 Expr的ype是否是boo类型的。语义分析的例子  Type equivalence and compatibility  Two base types are equivalent if and only if they are the same exact type.  BoolExpr : Expr { $$ = CheckBoolExprUsage(&@1, $1); }  CheckBoolExprUsage()中检查$1即 Expr的type是否是bool类型的