# an iterative SR program for approximating the integral
# of f(x) from 0.0 to 20.0 for f(x) = sin(x)*exp(x)

resource quad()

  var intervals: int; getarg(1, intervals)
  var area := 0.0
  var step := 20.0/intervals    # distance between intervals
  var fleft := sin(0.0)*exp(0.0), fright: real
    # fleft is used to compute f(x) just once per value of x

  var start := age()    # start time

  fa x := 0.0 to 20.0-step by step ->
      fright := sin(x+step)*exp(x+step)
      area +:= (fleft+fright)*step/2    # trapezoidal rule
      fleft := fright
  af
  var finish := age()    # finish time

  write("intervals =",intervals," area =",area,
        " time = ",finish-start)

end