You can use the functions of the module Control.Arrow.ArrowIf of the hxt package. Here you find the function ifA, a lifted version of the if-else-statement. For example the code
if (True) then getAttrValue "rdf:about" else getAttrValue "rdf:ID"
should be written as
ifA (constA True) (getAttrValue "rdf:about") (getAttrValue "rdf:ID")
Depending of what you want to archive, you should use derived functions of ifA
like guards.