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% File src/library/tools/man/vignetteEngine.Rd
% Part of the R package, https://www.R-project.org
% Copyright 2013-2019 R Core Team
% Distributed under GPL 2 or later

\name{vignetteEngine}
\alias{vignetteEngine}
\title{Set or Get a Vignette Processing Engine}
\description{
Vignettes are normally processed by \code{\link{Sweave}}, but package
writers may choose to use a different engine (e.g., one provided by the
\CRANpkg{knitr}, \CRANpkg{noweb} or \CRANpkg{R.rsp} packages).  This function
is used by those packages to register their engines, and internally by
\R{} to retrieve them.
}
\usage{
vignetteEngine(name, weave, tangle, pattern = NULL,
           package = NULL, aspell = list())
}
\arguments{
  \item{name}{the name of the engine.}
  \item{weave}{a function to convert vignette source files to PDF/HTML or
intermediate LaTeX output.}
  \item{tangle}{a function to convert vignette source files to \R code.}
  \item{pattern}{a regular expression pattern for the filenames handled
    by this engine, or \code{NULL} for the default pattern.}
  \item{package}{the package registering the engine.  By default, this
    is the package calling \code{vignetteEngine}.}
  \item{aspell}{a list with element names \code{filter} and/or
    \code{control} giving the respective arguments to be used when spell
    checking the text in the vignette source file with
    \code{\link{aspell}}.}
}
\details{
If \code{weave} is missing, \code{vignetteEngine} will return the currently
registered engine matching \code{name} and \code{package}.

If \code{weave} is \code{NULL}, the specified engine will be deleted.

Other settings define a new engine. The \code{weave} and \code{tangle}
functions must be defined with argument lists compatible with
\code{function(file, ...)}. Currently the \code{...} arguments may
include logical argument \code{quiet} and character argument
\code{encoding}; others may be added in future. These are described in
the documentation for \code{\link{Sweave}} and \code{\link{Stangle}}.

The \code{weave} and \code{tangle} functions should return the
filename of the output file that has been produced. Currently the
\code{weave} function, when operating on a file named
\file{<name><pattern>} must produce a file named
\file{<name>[.](tex|pdf|html)}. 
The \file{.tex} files will be processed by \command{pdflatex} to
produce \file{.pdf} output for display to the user; the others will be
displayed as produced.  The \code{tangle} function must produce a file
named \file{<name>[.][rRsS]} containing the executable \R{} code from
the vignette.  The \code{tangle} function may support a
\code{split = TRUE} argument, and then it should produce files named
\file{<name>.*[.][rRsS]}.

The \code{pattern} argument gives a regular expression to match the
extensions of files which are to be processed as vignette input files.
If set to \code{NULL}, the default pattern \code{"[.][RrSs](nw|tex)$"}
is used.
}
\value{
  If the engine is being deleted, \code{NULL}.  Otherwise a list
  containing components
  \item{name}{The name of the engine}
  \item{package}{The name of its package}
  \item{pattern}{The pattern for vignette input files}
  \item{weave}{The weave function}
  \item{tangle}{The tangle function}
}
\author{
Duncan Murdoch and Henrik Bengtsson.
}
\seealso{
\code{\link{Sweave}} and the \sQuote{Writing R Extensions} manual.
}
\examples{
str(vignetteEngine("Sweave"))
}
\keyword{utilities}
\keyword{documentation}