XSLT is great fun as a general functional programming language! You can build native functional data-structures[1], implement graph-traversal algorithms[2], and even write test assertions[3]!
1: https://github.com/pjlsergeant/xslt-fever-dream/blob/main/ut...
2: https://github.com/pjlsergeant/xslt-fever-dream/blob/main/ut...
3: https://github.com/pjlsergeant/xslt-fever-dream/blob/main/ut...
Files are missing from the repo(?). What about util-map.xsl, test-map.xsl, util-serialize.xsl