用 Rust 实现整数的带括号四则运算： 四则运算的 EBNF 定义如下：

Expression ::= (Expression [+-])? PriorityExpression
PriorityExpression ::= (PriorityExpression [*/])? Factor
Factor ::= Number | "(" Expression ")"

消除左递归，转化为 LL(1) 文法：

Expression ::= PriorityExpression ExpressionTail
ExpressionTail ::= ([+-] PriorityExpression ExpressionTail)?
PriorityExpression ::= PriorityExpression PriorityExpressionTail
PriorityExpressionTail ::= ([*/] Factor PriorityExpressionTail)?
Factor ::= Number | "(" Expression ")"

Railroad Diagram 如下：

Expression:

PriorityExpression:

Factor:

相关 Railroad Diagram 在这个网站生成 https://www.bottlecaps.de/rr/ui