true[false] doesn't return ()

Same for true[2], null[2], false[2]

It seems to be a problem in the parser.

For the query 'true[false()]', I get the following AST

<ParseNodeTree>
<MainModule pos='/home/mbrantner/zorba/build/../build/tmp.jq:1.2-15' ptr='0x1ba4a20'>
  <QueryBody pos='/home/mbrantner/zorba/build/../build/tmp.jq:1.2-15' ptr='0x1b693d0'>
    <BooleanLiteral pos='/home/mbrantner/zorba/build/../build/tmp.jq:1.2-15' ptr='0x1b7e220'>
    </BooleanLiteral>
  </QueryBody>
</MainModule>
</ParseNodeTree

which seems to completely miss the predicate.

For the query 'true()[false()] it works.

Can you clarify what this is supposed to do? First, I assume this is JSONiq syntax, yes? Second, is the use of [] an array index? If yes, I assume then it's supposed to return () because the thing to which the [] is applied isn't an array, yes? If that's true, then why isn't it an error?

true[2] is JSONiq
true()[2] is XQuery

The latter works. The former doesn't. Please compare the resulting parse trees to see how it should be.

When it's just "true," it's not considered a function call because function calls must have (...) after them. Should the "true" be considered a synonym for "true()" in JSONiq?

The problem is that it reduces by the wrong rule. At the StepExpr rule (line 4317, parser.y), it chooses:

    AxisStep -> ForwardStep (AbbrevForwardStep -> NodeTest -> NameTest -> QName) PredicateList

rather than:

    PostfixExpr -> PostfixExpr (PrimaryExpr) -> PredicateList

When "true()" is used, it parses as:

    PrimaryExpr -> FunctionCall

without the "()", it fails to match PrimaryExpr. So that's the problem, but it's not clear how to fix it. Suggestions?