Antlr4相互左递归错误

Question

I prepared a grammar for a mini language I am creating, but I am getting a mutual left recursion error between var and functioncall

var
: NAME
| var '[' exp ']'
| var '.' var
| functioncall '.' var
;
functioncall
: NAME '(' (exp)? (',' exp)* ')'
| var '.' functioncall
| functioncall '.' functioncall
;

specifically at var : functioncall '.' functioncall var : functioncall '.' functioncall and functioncall : var '.' functioncall functioncall : var '.' functioncall which basically corresponds to somefunction().var and instanceofClass.function() .

Is there any way I can achieve this?

Edit : Grammar should also allow something like var '=' exp where var can be instance.var or function().var

Answer 1

Antlr 4 (and not before that) can handle both-side recursion in the same rule. So something like

expr: expr '+' expr | NUMBER

is valid.

So we can put another new rule to abstract either a var or a function call.

value
: var
| functioncall
| value '.' value
;

var
: NAME
| var '[' exp ']'
;

functioncall
: NAME '(' exp? (',' exp)* ')'
;

Not only the grammar is simpler to parse (to human readers), but now you have no mutual recursion.

Note: untested.