如何从语法规则中删除左递归

Question

以下一组 antlr 语法行给出了 number_operation & number_argument 的错误，如下所示

The following sets of rules are mutually left-recursive

number_funtion : COUNT LEFT_PAREN number_argument RIGHT_PAREN

number_operation : 
number_argument (number_operator number_argument)+ | LEFT_PAREN number_argument (number_operator number_argument)+ RIGHT_PAREN 
| prefix_operator number_argument | LEFT_PAREN prefix_operator number_argument RIGHT_PAREN;

number_argument : number_column | number_function | digit_constant | number_operation ;

为了避免左递归，用 number_argument 的每个元素的所有可能组合修改 number_operation 可以像下面那样完成，但是会导致更长的规则。

number_operation :
number_column (number_operator number_argument)+ | LEFT_PAREN number_column (number_operator number_column)+ RIGHT_PAREN
| prefix_operator number_column | LEFT_PAREN prefix_operator number_column RIGHT_PAREN
//and other combinations

有人可以建议在这里删除左递归的最佳方法是什么吗？

Answer 1

这样的事情怎么样：

number_operation
 : number_operation (number_operator number_argument)+
 | number_argument_2 (number_operator number_argument)+
 | LEFT_PAREN number_argument (number_operator number_argument)+ RIGHT_PAREN
 | prefix_operator number_argument
 | LEFT_PAREN prefix_operator number_argument RIGHT_PAREN
 ;

number_argument
 : number_column
 | number_function
 | digit_constant
 | number_operation
 ;

number_argument_2
 : number_column
 | number_function
 | digit_constant
 ;

?

如何从语法规则中删除左递归

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