Re: [basex-talk] A question about the arrow operator and predicates

Dear Bridger,

I was wondering if anyone would have an insight for me as to why the following expression is wrong:

for $s in ("/a/b/c", "/1/2/3") let $t := $s => tokenize("/")[last()] return $t

This is due to the grammar rules of XQuery 3.1, which mandate that “=>” is followed by an “ArrowFunctionSpecifier” and an “ArgumentList”. Here are some production rules from the spec:

[96] ArrowExpr ::= UnaryExpr ( "=>" ArrowFunctionSpecifier ArgumentList )* [127] ArrowFunctionSpecifier ::= EQName | VarRef | ParenthesizedExpr [122] ArgumentList ::= "(" (Argument ("," Argument)*)? ")" …

The arrow function specifier can be an EQName, a variable reference or a parenthesized expression. The last one will do the job:

for $s in ("/a/b/c", "/1/2/3") let $t := ($s => tokenize("/"))[last()] return $t

Hope this helps, Christian

[1] https://www.w3.org/TR/xquery-31/#id-arrow-operator

Thanks for your help! Best, Bridger

PS I don't always remember to look at the optimized query in the Info window, but when I do I always get a hint about something; "util:last()" in this case.

correctly

for $s in ("/a/b/c", "/1/2/3")
let $t := tokenize($s, "/")[last()]
return $t

for $s in ("/a/b/c", "/1/2/3")
let $t := $s => tokenize("/") => util:last()
return $t