$s[NaN]
NaN:^try-catch{^s.double[]}
NaN:^try-catch{^s.double(0)}
$s[INFINITY]
Inf:^try-catch{^s.double[]}
Inf:^try-catch{^s.double(0)}

SQRT(-1):^try-catch{^math:sqrt(-1)}
POW(0;-1):^try-catch{^math:pow(0;-1)}

$x[^xdoc::create{<?xml version="1.0"?><x n=""/>}]
^try-catch{^x.selectNumber[number(/x/@n)]}