bisection <- function(expr, x = c(0, 1), TOL = 1e-6, print = FALSE) {
  hasZero <- function(a, b, expr = expr) (eval(expr, envir = list(x = a), enclos = parent.frame()) * eval(expr, envir = list(x = b), enclos = parent.frame())) < 0

  expr <- checkExpression(expr)
  if (length(x) != 2)
    stop("'x' should be a length-2 vector specifying an interval [a, b] containing root")

  a <- min(x)
  b <- max(x) 
  d <- getOption("digits")
  if (!hasZero(a, b))
    stop("Interval does not enclose root.")

  while ((b - a) / 2 > TOL) {
    c <- (a + b) / 2

    if (print) 
      print(sprintf("%.*f %.*f", d, c, d, (b - a) / 2), quote = FALSE)

    ifelse(hasZero(a, c), b <- c, a <- c)
  }  # end while loop
  
  return(c)
}  # end bisection