\name{as.function.formula}

\alias{as.function.formula}

\title{ Make a one-line function from a formula. }

\description{

  Create a function from a formula.

}

\usage{

\method{as.function}{formula}(x, ...)

}

\arguments{

  \item{x}{ Formula with no left side. }

  \item{\dots}{ Currently not used. }

}

\value{

  A function is returned whose formal arguments are the

  variables in the left hand side, whose body

  is the expression on the right side of the formula and whose 

  environment is the environment of the formula.  If there is

  no left hand side the free variables on the right, in the 

  order encountered are used as the arguments.  \code{letters},

  \code{LETTERS} and \code{pi} are ignored and not used as arguments.

  If there is no left hand side and 

  any of \code{..1}, \code{..2}, ..., \code{..9} are found

  as free variables then they are not used as arguments but \code{...} 

  is used as a trailing argument instead.

  If there is no left hand side and \code{`&`} is found as a free variable

  then that variable is used as the first argument and \code{...} is added

  as the last argument.

  If the left hand side is \code{0} then the function is created as

  a zero argument function.

}

\note{\code{->}, \code{->>}, \code{=}, \code{<-}, \code{<<-} and \code{?}

all have lower operator precdence than \code{~} so function bodies that

contain them typically must be surrounded with \code{{...}}.}

\seealso{ \code{\link[base]{Syntax}}.}

\examples{

old.options <- options(keep.source = FALSE)

as.function(~ as.numeric(x) + as.numeric(y))

as.function(x + y ~ as.numeric(x) + as.numeric(y)) # same

as.function(~ ..1 + ..2)

# the replacement function in gsubfn uses as.function.formula to

# interpret formulas as functions.  Here we insert ! after each digit.

gsubfn("[0-9]", ~ paste0(`&`, "!"), "ab4cd5") 

\dontrun{

# example where function body must be surrounded with {...} 

# due to use of <<-.  See warning section above.

assign("mywarn", NULL, .GlobalEnv)

fn$tryCatch( warning("a warning"), 

    warning = w ~ { mywarn <<- conditionMessage(w)})

print(mywarn)

}

options(old.options)

}

\keyword{ character }