Plotting A Mathematical Expression

plotcurve <-
  function(equation = "y = sqrt(1/(1+x^2))", ...){
    leftright <- strsplit(equation, split = "=")[[1]]
    left <- leftright[1] # The part to the left of the "="
    right <- leftright[2] # The part to the right of the "="
    expr <- parse(text=right)
    xname <- all.vars(expr)
    if(length(xname) > 1)stop(paste("There are multiple variables, i.e.",paste(xname,
                                                                               collapse=" & "),
                                    "on the right of the equation"))
    if(length(list(...))==0)assign(xname, 1:10)
    else {
      nam <- names(list(...))
      if(nam!=xname)stop("Clash of variable names")
      assign("x", list(...)[[1]])
      assign(xname, x)
    }
    y <- eval(expr)
    yexpr <- parse(text=left)[[1]]
    xexpr <- parse(text=xname)[[1]]
    plot(x, y, ylab = yexpr, xlab = xexpr, type="n")
    lines(spline(x,y))
    mainexpr <- parse(text=paste(left, "==", right))
    title(main = mainexpr)
  }

plotcurve()
plotcurve("ang=asin(sqrt(p))", p=(1:49)/50)