r - Why does plot not respect add = TRUE? -

why r's base plot function this? have use points or lines, needs special code rather using type argument.

plot(1:10) plot(10:1, add = true) warning messages: 1: in plot.window(...) : "add" not graphical parameter 2: in plot.xy(xy, type, ...) : "add" not graphical parameter 3: in axis(side = side, @ = at, labels = labels, ...) : 

etc.

many packages provide methods (i.e. "override") plot , provide obvious ability plot(obj, add = true) long obj of appropriate class. (examples sp, raster, spatstat.)

is there reason plot.default not already?

edit: discussed @ length here:

http://tolstoy.newcastle.edu.au/r/e4/devel/08/03/0725.html

dm answers here: http://tolstoy.newcastle.edu.au/r/e4/devel/08/03/0734.html

because plot.default doesn't have add argument

> args(plot.default) function (x, y = null, type = "p", xlim = null, ylim = null,      log = "", main = null, sub = null, xlab = null, ylab = null,      ann = par("ann"), axes = true, frame.plot = axes, panel.first = null,      panel.last = null, asp = na, ...)  null 

those other functions not overriding plot providing own methods, have argument add because written way. personally, having grown using points() , lines() etc don't find them work , use them in preference plot method add argument, although we've written both ways in packages contribute to.

as why plot.default doesn't have add argument? you'd have ask r core, can suggest reasons

1. plot.default designed generate entire plot on device
2. there points() , lines() etc why duplicate?
3. plot.default simpler code without code handle add
4. backwards compatibility s/s-plus