addXSLTFunctions: Queue R functions to registered as XSL functions.
In sckott/sxslt: R extension for libxslt

Description Usage Arguments Details Value Author(s) References See Also Examples

These functions allow one to set and query a list of functions maintained in R that will be registered with the R XSLT extension module each time it is initialized, i.e. each time a stylesheet that refers to the extension is applied to an XML document. The addXSLTFunctions allows one to add functions to the existing queue, and optionally to clear the existing contents (via the clear argument).

R functions registered in the default manner can be called from XSL but have little access to the state of the XSL transformation. However, an R function can arrange to be always called from XSL with an XSLTContext reference object as its first argument. This happens for the R functions that inherit from the S3-style class XSLTContextFunction. One can specify this as the class of a function or alternativel call xsltContextFunction in the call to register/add the R function.

getXSLTFunctions returns the current list of functions that are queued to be registered.

These functions are only useful if the default registration function is used. This is installed when the package is loaded but can be changed via SxsltInitializationFunction.

setXSLTFunctions is for use when we need to manipulate the list of functions such as when we want to remove just some of the functions. Be very cautious about using this. One has to know precisely which functions should be removed and which should be kept and there may be name conflicts which make this ambigious, e.g. instances of the same function with different environments.

addXSLTFunctions(..., .namespace = "r", .funcs = list(), clear = FALSE)
getXSLTFunctions()
setXSLTFunctions(funs)
xsltContextFunction(f)

`...`	a named list of R functions. Each name is used as the name in the XSLT extension module, i.e. the name by which the corresponding function can be called from within an XSL rule. This can be best used when calling the function interactively.
`.namespace`	a character string. This identifies the namespace for which the function is being added. The value can either be the prefix for the namespace, e.g. "r", or the namespace's full URI, e.g. "http://www.r-project.org".
`.funcs`	a named list of R functions that provides an alternative mechanism than the ... for specifying the functions. This is convenient for programatic use.
`clear`	a logical value which if `TRUE` first removes existing elements from the list of functions to be registered.
`f`	the function which is to be identified as an `XSLTContextFunction` instance.
`funs`	a named list of functions which are to be registered using the names in the list. This is often used to reset the entire collection of "global" functions that will be registered with the XSLT engine when it next starts to process a document.

This uses a closure within the name space to allow updates of the R list of functions.

Both functions return the current list of queued functions. addXSLTFunctions returns it invisibly to avoid the default printing.

xsltContextFunction returns an object of class XSLTContextFunction.

Duncan Temple Lang <duncan@wald.ucdavis.edu>

http://www.omegahat.org/Sxslt http://www.xmlsoft.org/XSLT

registration.R in the examples/ directory.

SxsltInitializationFunction xsltApplyStyleSheet

  addXSLTFunctions(foo = function(x) {
                            cat("in foo\n")
                            print(x)
                            x*2
                         },
                   bar = function(x,y) {
                            cat("in bar\n")
                            print(x)
                            print(y) 
                            nchar(x) + nchar(y)
                         },
                   vars = xsltContextFunction(
                             function(ctxt) {
                                cat("xsl variable bob has value", getXSLVariables(ctxt, "bob"), "\n")
                             })
   )

  xsltApplyStyleSheet(system.file("examples", "register.xml", package = "Sxslt"),
                      system.file("examples", "register.xsl", package = "Sxslt"), FALSE)

  addXSLTFunctions(Date = date)