call-func-with-expressionlist.R

`%(%` <- function(fn, args) {
  fn <- substitute(fn)
  args <- as.list(substitute(args))
  if(!identical(args[[1]], quote(`{`)))
    stop("right hand side must be an expressionlist starting with a `{`")

  args[[1L]] <- NULL
  nms <- names2(args)
  for(i in seq_along(args)) {
    ar <- args[[i]]
    if(is.call(ar) && identical(ar[[1L]], quote(`=`))) {
      if(!is.symbol(nm <- ar[[2L]])) stop("Left hand side of `=` must be named")
      nms[i] <- as.character(nm)
      args[i] <- ar[3L] 
    }
  }
  names(args) <- nms

  if (is.call(fn) && is.symbol(fn[[1L]]) &&
      grepl("^%.+%$", as.character(fn[[1L]]))) {
    fn[[3L]] <- as.call(c(fn[[3L]], args))
    return(eval.parent(fn))
  }

  # else fn is a symbol or a function meant to be called normally
  eval.parent(as.call(c(fn, args)))
}