How to enforce use of parentheses? (no operator precedence)

[hasanayan]

Here is my current query rule:

public query = this.RULE('query', () => {

    this.SUBRULE2(this.expression, { LABEL: 'lhs' });

    this.MANY1({
      DEF: () => {
        this.SUBRULE1(this.logicalOp);
        this.SUBRULE3(this.expression, { LABEL: 'rhs' });
      },
    });
  });

we initially used "operator precedence" and this rule worked fine for us. However, now we want to get rid of operator precedence and force users to use only one type of logical operator (allow A AND B AND C AND D... but not A AND B AND C OR D ...) so that they will have to put parentheses to group their queries. Could you please help me how to translate this rule into my CstParser method?

[NaridaL]

Something like this would probably work:

public query = this.RULE("query", () => {

  this.SUBRULE2(this.expression, { LABEL: "lhs" })

  // save the first operator so we can check that later operators match it.
  let operator = undefined
  this.MANY1({
    DEF: () => {
      operator = this.OR([
        {
          GATE: () => operator === undefined || operator === AND,
          ALT: () => this.CONSUME(TOKEN.AND)
        },
        {
          GATE: () => operator === undefined || operator === OR,
          ALT: () => this.CONSUME(TOKEN.OR)
        }
      ])
      this.SUBRULE3(this.expression, { LABEL: "rhs" })
    },
  })

You can also probably solve it without the OR having a branch for every operator, but this way you will probably get better error messages.

[hasanayan]

yup, that did it. Thanks!

[bd82]

Hello @hasanayan

You can also evaluate modeling this restriction in a post parsing phase.
Basically as a semantic role rather than a syntactic rule.

In other words you could think of this as a formatting / linting rule instead of
a basic part of the language.