Surely you jest.

No. I was deadly serious, though I agree that I was technically wrong when I said: And IMO, that totally negates any claim that XSLT is a FP language.. I would be completely wrong were in not for the IMO.

You suggested above that the OP needn't learn another FP language as he had already experienced them through XSLT. As I tried to explain, I also used XSLT long before I ever used any other FP language, and before I knew what FP languages were about. Now, having dabbled in several FP languages, it had never even crossed my mind that XSLT was in anyway related.

I guess that's because all the FP languages (except XSLT) that I have tried, seem to have a common set of typifying characteristics (as opposed the defining characteristics), that (IMO) are more relevant to their power and utility, and especially to the way they influence the thought patterns of the programmer.

Amongst that set of typifying characteristics I would include, conciseness, composability and extensible syntax as the primary ones that have affected my way of coding. And the way I think about coding.

You see, other than those in pursuit of academic knowledge and perhaps CS achievements, I don't think that the defining characteristics, referential transparency, immutability, mathematical provability, are anywhere near as important to the working programmer as writeability, maintainability and whether it gets the job done quickly and easily.

So yes, XSLT is a (dysfunctional) FP language. But no, I do not think that having used it is in any way a substitute for using a proper FP language. Especially for the way the latter influences ones way of thinking and working.