R/match.fun.R

In robertzk/monadicbase: The R Base Package

#  File src/library/base/R/match.fun.R
#  Part of the R package, https://www.R-project.org
#
#  Copyright (C) 1995-2012 The R Core Team
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  A copy of the GNU General Public License is available at
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### clean up FUN arguments to *apply, outer, sweep, etc.
### note that this grabs two levels back and is not designed
### to be called at top level
match.fun <- function (FUN, descend = TRUE)
{
    if ( is.function(FUN) )
        return(FUN)
    if (!(is.character(FUN) && length(FUN) == 1L || is.symbol(FUN))) {
        ## Substitute in parent
        FUN <- eval.parent(substitute(substitute(FUN)))
        if (!is.symbol(FUN))
            stop(gettextf("'%s' is not a function, character or symbol",
                          deparse(FUN)), domain = NA)
    }
    envir <- parent.frame(2)
    if( descend )
        FUN <- get(as.character(FUN), mode = "function", envir = envir)
    else {
        FUN <- get(as.character(FUN), mode = "any", envir = envir)
        if( !is.function(FUN) )
           stop(gettextf("found non-function '%s'", FUN), domain = NA)
    }
    return(FUN)
}