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% File src/library/methods/man/LanguageClasses.Rd
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2008 R Core Team
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% Distributed under GPL 2 or later
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\name{language-class}
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\title{Classes to Represent Unevaluated Language Objects}
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\docType{class}
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\alias{language-class}
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\alias{(-class}
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\alias{<--class}
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\alias{call-class}
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\alias{for-class}
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\alias{if-class}
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\alias{repeat-class}
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\alias{while-class}
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\alias{name-class}
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\alias{\{-class}
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\description{  The virtual class \code{"language"} and the specific
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  classes that extend it represent unevaluated objects, as produced for
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  example by the parser or by functions such as \code{\link{quote}}.
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}
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\usage{
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### each of these classes corresponds to an unevaluated object
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### in the S language.
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### The class name can appear in method signatures,
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### and in a few other contexts (such as some calls to as()).
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"("
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"<-"
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"call"
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"for"
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"if"
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"repeat"
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"while"
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"name"
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"{"
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### Each of the classes above extends the virtual class
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"language"
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}
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\section{Objects from the Class}{
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  \code{"language"} is a virtual class; no objects may be created from
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  it.
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  Objects from the other classes can be generated by a call to
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  \code{new(Class, ...)}, where \code{Class} is the quoted class name, and
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  the \dots arguments are either empty or a \emph{single} object that is
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  from this class (or an extension).
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}
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\section{Methods}{
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  \describe{
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    \item{coerce}{\code{signature(from = "ANY", to = "call")}.  A method
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      exists for \code{as(object, "call")}, calling \code{as.call()}. }
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  }
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}
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\examples{
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showClass("language")
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is( quote(sin(x)) ) # "call"  "language"
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(ff <- new("if"))  ; is(ff) # "if" "language"
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(ff <- new("for")) ; is(ff) # "for" "language"
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}
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\keyword{classes}