We propose X-Fun, a higher-order functional programming language for transforming XML documents based on path queries. We present a lean formal model for the operational semantics of X-Fun based on lambda calculus and provide an in-memory implementation on top a chosen XPath evaluator. We also discuss compilers from XSLT, XQuery and XProc into X-Fun, which leads us to in-memory implementations of these XML standards with large coverage and high efficiency.

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