Hello,

I use BaseX mostly for boolean queries, I have a hardware database and I check if specific hardware support features I need.

It works great but when something is not as expected, it's hard to find out the reason.

E.g. given an expression like:

$some-value = $some-list and (custom:predicate() or $x > $y)

I would like to know why it's true or false.

For now I add trace() manually on the subexpressions, rerun, add trace to more specific parts, etc.

Ideally I would want to break down the query execution so it shows the values of subparts of the query to pinpoint why it is false, e.g. have an output like:

$some-value = $some-list and (custom:predicate() or $x > $y) -> false()

$some-value = $some-list -> true()

$some-value -> 1

$some-list -> (1, 2, ..., 10)

custom:predicate() or $x > $y -> false()

custom:predicate() -> false()

... # It should also go inside the function

$x > $y -> false()

$x -> 10

$y -> 11

Any ideas how it could be achieved?

Looking at the code, maybe a debug() (like iter() or item()) method could be added to Expr objects which would trace the expression query, file, line and the result of the expression (or probably the first x characters of the result to avoid huge output)? With an xquery function which would trigger it.

I also thought of modifying the query programmatically to add trace() calls but that seems overly complicated.

Best regards,

Iwan