R/yacmode.R

In Ryacas0: Legacy 'Ryacas' (Interface to 'Yacas' Computer Algebra System)

#' yacmode interface
#' 
#' Interactive interface to the yacas
#' 
#' The user types valid yacas input and presses return. Type 'quit' to return
#' to R prompt.
#' 
#' 
#' @param enable_history Use `R` history such that previous yacas commands can be used. Default is `TRUE`.
#' @return Output of yacas is returned.
#' @note Note that command will use R `history()` and modify it by default. 
#' Yacas is given a limited amount of time to complete, otherwise
#' `\[1\] CommandLine(1) : User interrupted calculation` is returned. E.g.
#' Taylor(x,0,5) 1/(1+x) will work, but Taylor(x,0,12) 1/(1+x) is likely to
#' take too long.
#' @references \url{http://www.yacas.org/}
#' @keywords symbolmath
#' @examples
#' 
#' \dontrun{
#' yacmode()
#'  (x+y)^3-(x-y)^3
#'  Simplify(%)
#'  q
#' }
#' 
#' @importFrom utils loadhistory savehistory
#' @return invisible NULL
#' @export
yacmode <- function(enable_history = TRUE) {
  # Enable history in yacmode()
  # https://stackoverflow.com/a/27528113
  if (enable_history == TRUE) {
    tmphistory <- tempfile()
    try(utils::savehistory(tmphistory), silent = TRUE)
    on.exit(unlink(tmphistory))
  }
  
  update_history <- function(x) {
    # Update history:
    if (enable_history == TRUE) {
      histcon <- file(tmphistory, open = "a")
      writeLines(x, histcon)
      close(histcon)
      try(utils::loadhistory(tmphistory), silent = TRUE)
    }
    
    return(invisible(x))
  }

  
  cat("Enter Yacas commands here. Type quit to return to R\n")
  x <- readline("Yacas->")
  
  while (length(which(c("stop;", "stop", "end;", "end", "quit;",
                        "quit", "exit;", "exit", "e;", "e", "q;", "q", "q()", "\n") == x)) ==
         0) {

    # Put here to not include exit/quit/... in history
    update_history(x)
    
    o <- yacas(x)
    print(o)
    
    # Old:
    # x <- gsub("Out>","#",x)
    # x <- gsub(" ","",unlist(strsplit(x,"#"))[1])
    # x <- gsub(" ","",gsub("In>",'',x))
    # if (x != '' && !is.na(x)){
    #   pr <- try( parse(text = x ),silent=TRUE)
    #   if (class(pr)=='try-error'){
    #     # o<- yacas(x,retclass='character');
    #     o<- yacas(x)
    #   } else {
    #     o <- yacas(parse(text = x)); 
    #   }
    #   # o <- paste(o)
    #   # a<-lapply(o,function(s) cat(paste(s,"\n")))
    #   print(o)
    # }
    
    x <- readline("Yacas->")
  }
  
  return(invisible(NULL))
}