Create a session variable from a response

I tried to do this with EL but couldn't, so I move the code to scala but neither work.
The main idea is this one:

I get a value (142) from a response and sent it to a var called valorreq1 (OK, worked)

.check(xpath("/env:Envelope/env:Body/ns1:EResponse/Lista/Opcion/Valor", List("env" -> "", "ns1" -> "")).saveAs("valorreq1")))

So I need also, the length of this value into a variable called valorreq1L 

Both variables will be used in a feed in a ElBodyFile:


So far so good, but:

Using this in EL:

$(fn:length(valorreq1) didn't work.

So I move the conversion to:

			session => session("valorreq1L", 12345)
		but can't set this variable with the lenght of the valorreq1.
		In other works, I need something like this:
			session => session("valorreq1L", fn:length(valorreq1) )

Any suggestions or idea? Thanks in advance and kind regardas