在antlr 3中相互左递归

Question

我尝试在antlr 3中解析语法，但是左递归存在问题，并且我是解析语法的初学者。

Answer 1

The problem is that the roules b, e, t, f are referencing each other without consuming any input - eg a number could be accepted by multiple sequences:

b -> NUM
b -> e -> t -> f -> b -> NUM
...

the cycle you have there probably is meant to express a sub-expression - what's missing there then are parentheses:

start   : e;
e       : t (a t)*;
t       : f (m f)*;
f       : ID | NUM | '-'NUM | '(' e ')';
a       : '+' | '-';
m       : '*' | '/';

(I also changed e : t | tat to e : t | eat to allow 1 + 2 + 3 )