R Under development (unstable) (2025-12-16 r89184 ucrt) -- "Unsuffered Consequences"
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> message("*** withPar() ...")
*** withPar() ...
> 
> library("R.devices")
R.devices v2.17.3 successfully loaded. See ?R.devices for help.
> 
> x <- 1
> message("x=", x)
x=1
> 
> withPar({
+   layout(1:4)
+ 
+   x <- c(x, 2)
+   message("x=", x)
+   stopifnot(all(x == 1:2))
+ 
+   withPar({
+     plot(1:10)
+     plot(10:1)
+     x <- c(x, 3)
+     message("x=", x)
+   }, pch=4)
+   message("x=", x)
+   stopifnot(all(x == 1:3))
+ 
+   withPar({
+     plot(1:10)
+     plot(10:1)
+     x <- c(x, 4)
+     message("x=", x)
+   }, pch=0, bg="yellow")
+   message("x=", x)
+   stopifnot(all(x == 1:4))
+ 
+   x <- c(x, 5)
+   message("x=", x)
+   stopifnot(all(x == 1:5))
+ }, mar=c(2,2,1,1))
x=12
x=123
x=123
x=1234
x=1234
x=12345
> 
> message("x=", x)
x=12345
> stopifnot(all(x == 1:5))
> 
> 
> # Graphical parameters set "manually" are also reset
> opar <- par()
> withPar({
+   par(pch=4L, lwd=3)
+   plot(1:10)
+ })
> stopifnot(all.equal(par(), opar))
> 
> message("*** withPar() ... DONE")
*** withPar() ... DONE
> 
> proc.time()
   user  system elapsed 
   0.45    0.12    0.56