Saxon

I have implemented the basic changes to achieve this (on the 9.7 branch, not yet committed), and it is working - except for export.

The design uses a CurriedSystemFunction in the same way as similar optimizations for translate, format-number, etc. But the code for exporting and importing calls to a CurriedSystemFunction is very ad-hoc so I made changes here - the idea is to export the function call as if the optimization had not taken place, and then repeat the optimization on import. At present the XSLT3 type tests are crashing when run with -export.

The problem is in establishing correct bindings between components and I suspect the problem is that the "original function call" which we are exporting in place of the curried call includes subexpressions that have the wrong binding slot number.

I think I have fixed these problems. A CurriedSystemFunction now has to provide a method to export itself as if it were the original function call. The package loader calls the same method (fixArguments()) as the optimizer to re-optimize the function call into its curried form.

Having got this working, I have a feeling it might all be over-complex. The regex functions like matches() manage pre-evaluation of the regular expression without any of this complexity, simply by computing the redundant data during SystemFunction.makeFunctionCall().

I've decided to follow a different approach. Rather than making key() use a CurriedSystemFunction (which is currently used by translate() and format-number()), I've scrapped CurriedSystemFunction (which creates a lot of complexity for stylesheet exporting) and these functions now optimize themselves simply by putting data in local fields within the SystemFunction object (an approach which works perfectly well for the regular expression functions).

At present this is giving some failures on XSLT format-number tests.

Now seems to be working. There are a few test failures with -export but I don't think they are related. Not yet committed. Need to copy the changes to the 9.8 branch.