"If kitchen appliances were like programs"

    If kitchen appliances were like programs, they would all look
    alike sitting on  the  counter. They would all be gray, featureless 
    boxes, into which one places  the food to be processed. The door
    to the box, like the box itself, is completely opaque.

    On  the  outside of each box is a general description of what the
    box does. For  instance,  one box might say: "Makes anything a
    meal"; another: "Cooks perfectly every time"; another: "Never more
    than 100 calories a serving". You  can  never  be  exactly  sure
    what happens to food when it is placed in these  boxes.  They 
    don't work with the door open, and the 200-page user's manual
    doesn't give any details.

    Working  in  a  kitchen  would  be  a  matter of becoming familiar
    with the idiosyncrasies of a small number of these boxes and then
    trying to get done what you really want done using them. For
    instance, if you want a fried-egg sandwich,  you  might try the
    "Makes anything a meal" box, since a sandwich is  a sort of meal.
    But because you know from past experience that this box leaves 
    everything  coated  with grease,  you  use  the "Never more than
    100 calories"  box  to  postprocess  the output. And so on. the
    result is never what you really want, but it is all you can do.

    You  aren't allowed to look inside the boxes to help you do what
    you really want  to do. Each box is sealed in epoxy. No one can
    break the seal. If the box  seems  to  not  be  working  right, 
    there is nothing you can do. Even calling  the manufacturer is no
    help, because the box is not under warranty to be for for any
    particular purpose. The manufacturers do have help lines, but  not 
    for  help with broken boxes--rather to help you figure out how to
    use  functioning  boxes.  But  don't  try  to  ask  how your box
    works. The help-line people don't know, or if they do, they won't
    tell you.

    Several  times a year you get a letter from the manufacturer
    telling you to ship  them your old box and they will send you a
    new one. If you do so, you find  yourself  with  a  shinier  box, 
    which does whatever it did before a little  faster,  or perhaps it
    does a little more--but since you were never sure what it did
    before, you  cannot be sure it's better now.
    {"Source Code" by Mark Weiser, IEEE Computer November 1987}