Recursive expression with optional parentesis.

Lezer
1

How to define recursive arithmetical expression with optional parenthesis in Lezer?
I try this:

@top Template { statement* }

statement {
    ArithExpr
}

ArithExpr {
    ArithExpr ArithOp ArithExpr |
    '(' ArithExpr ')' |
    number
}

ArithOp { '+' | '-' | '*' | '/' }

@tokens {
    number { @digit+ }
}

@detectDelim

but got an error:

shift/reduce conflict between
  ArithOp -> · "+"
and
  ArithExpr -> ArithExpr ArithOp ArithExpr
With input:
  ArithExpr ArithOp ArithExpr · "+" …
The reduction of ArithExpr is allowed before "+" because of this rule:
  ArithExpr -> ArithExpr · ArithOp ArithExpr
Shared origin: statement+ -> · ArithExpr
  via ArithExpr -> ArithExpr ArithOp · ArithExpr
    via ArithExpr -> ArithExpr · ArithOp ArithExpr
      ArithOp -> · "+"

and don’t understand how to resolve that.
Could you please help?
BTW, the similar grammar works in ANTLR v4.

2

It doesn’t know whether to parse 1 + 1 + 1 as (1 + 1) + 1 or 1 + (1 + 1). See the use of precedences in the binary expressions in the JavaScript example for a possible solution.

Without specifying precedence? I haven’t tried, but from what I know about ANTLR, I doubt that is correct.

3

Yes, ANTLR resolves ambiguities in favor of the alternative given first, and by default associates operators left to right.
Thank you for the answer, gonna look into the JS grammar.