# Higher-Order XSLT hoxsl is a library for XSLT 2.0, written in pure XSLT, introducing various types of higher-order logic; this includes higher-order functions and XSLT templates that take XSLT as input and produce XSLT as output. The system is fully tested---see the test cases for additional documentation as this project gets under way. This README will serve as an informal manual until official documentation is produced. ## Higher-Order Functions [Higher-order functions][xslt-30-ho] are a part of XSLT 3.0, but implementations that support them (such as Saxon) hide it behind proprietary versions of their software. Others still may wish to continue using XSLT 2.0. There are various approaches/kluges for this problem in earlier versions of XSLT; the basis of this implementation is motivated by Dimitre Novatchev's work on [higher-order functions in FXSL][nova-ho]. For example, consider an implementation of a filter function that accepts a node set and a predicate: ```xml ``` We could then apply a filter using this predicate like so: ```xml ``` hoxsl takes this a step further by providing a stylesheet to generate the boilerplate necessary for functions to be able to be applied using `f:apply`, as shown above. Applying `tranform/apply-gen.xsl` to the XSL stylesheet containing the above function definitions would produce output that can be directly imported (as a stylesheet); no additional work is needed. This can be included as part of a build process, and the output included within a distribution. ### Partial Applications Dynamic function applications using `f:apply` are partially applied if the number of arguments provided is less than the arity of the target function. For convenience, the `apply-gen` stylesheet will also generate functions to perform partial application without the use of `f:apply` for the first call, as in the first example below: ```xml ``` The implementation of partial function applications avoids the complexity and inaccuracies of [Novatchev's approach][nova-ho] by using only sequences, allowing arguments to retain their type and context. ## License This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. [nova-ho]: http://conferences.idealliance.org/extreme/html/2006/Novatchev01/EML2006Novatchev01.html [xslt-30-ho]: http://www.w3.org/TR/xslt-30/#dt-higher-order-operand