[basex-talk] UnaryLookup expression failure

30 Oct 2017

      While testing some XQuery lookup expressions on BaseX 8.6.7, I got a wrong 
result for this one:

      (map{'a':(1,3)},map{'a':(2,4)})!?a[2]

It should have returned the second item of the 'a' entry for each of the maps,
i.e.

      3 4

but it returns just

      3

Apparently the predicate is applied as if everything before it was in
parentheses, i.e. as if it were

      ((map{'a':(1,3)},map{'a':(2,4)})!?a)[2]

The (simplified) parse tree for the original expression and the XQuery 3.1
grammar however indicates that the predicate is part of the mapping target
expression:

     <SimpleMapExpr>
         <ParenthesizedExpr>
            ...
         </ParenthesizedExpr>
         <TOKEN>!</TOKEN>
         <PostfixExpr>
            <UnaryLookup>
               <TOKEN>?</TOKEN>
               <NCName>a</NCName>
            </UnaryLookup>
            <Predicate>
               <TOKEN>[</TOKEN>
               <IntegerLiteral>2</IntegerLiteral>
               <TOKEN>]</TOKEN>
            </Predicate>
         </PostfixExpr>
      </SimpleMapExpr>

Best regards
Gunther

[basex-talk] UnaryLookup expression failure

Gunther Rademacher