..... <- function(prompt="\n[hit enter to continue]: ") {
    cat(prompt, sep='')
    invisible(readline())
}

demo.me <- function(title, expr.str) {
    cat(title, "\n", rep('=', nchar(title)), "\n", sep='')

    cat('R> ', expr.str, sep='')
    .....("\n[Enter to execute]: ")

    cat(eval(parse(text=expr.str)), sep=' ')
    .....("\n\n")
}

# Set default margins for plotting (only slightly different from the default)
par(mar=c(5, 5, 4, 2))

Ns = 1:7
Squares = Ns^2

demo.me("A range", 'Ns = 1:7')

demo.me("Squares of range", 'Squares = Ns^2')

demo.me(
	"Plot squares of range",
        'plot(Squares)'
)

demo.me(
	"Nicer red N-sqared sized circles",
        'plot(Squares, pch=20, col="red", cex=Ns*5)'
)


demo.me(
	"Add title, labels, fix y-axis-labels to horizontal",
	'plot(Squares, pch=20, col="red", cex=Ns*5,
        main="nirvana", cex.main=3, las=1,
        xlab="N", ylab="N^2",
        cex.lab=1.25, font.lab=4)'
)

demo.me(
	"Add a grid",
	'grid(col="#888888")'
)

demo.me(
	"Add blue bulls-eye",
	'points(Squares, pch=19, col="blue", cex=Ns)'
)

demo.me(
	"Add black circles around circles",
	'points(Squares, pch=21, col="black", cex=Ns*4)'
)

demo.me(
	"Add orange dashed lines connecting the centers",
	'lines(Squares, col="orange", lwd=4, lty=3)'
)

demo.me(
	"Wow!!!",
 	'text(2.5, 30, "Wow!!!", col="#cc0044", cex=2.5, font=4)'
)