The Apraphul Rope Computer Simulator is based on an article by A. K.

  Dewdney (Mathematical Recreations, Scientific American, April 1988, v. 258

  No. 4, Pp. 118-121). He describes a mythical computer build out of ropes and

  springs. This program simulates such a computer.

       The basic unit of the computer is a box. Each box can have an output

  value of either 0 or 1. There are four kinds of box. NULL boxes have one

  input, the output equals the input. INVERT boxes have one input, the output

  is the opposite of the input. AND boxes have two inputs, the output is 1

  only if both inputs are 1. OR boxes have two inputs, the output is 1 if

  either input is 1.

       The program implements an 8x8 array of these boxes. Each box can take

  input from the column to the left and give output to the column on the

  right. The leftmost column takes input from the rightmost. Each box can take

  input or give output to the box in the same row, the box in the row above,

  or the box in the row below (the top row of boxes is connected to the bottom

  row).

       Programming the computer consists of specifying (1) what type of box

  each of the 64 boxes are, (2) which boxes are connected to which boxes, and

  (3) what inputs each box has initially.

       To specify these things use the arrow keys to move around from box to

  box. Type A (AND), I (INVERT), N (NULL), or O (OR) to change the box to this

  type.  Type 0 (both inputs false), 1 (top input true or only input true for

  NULL and INVERT boxes), 2 (bottom input true, not used for NULL or INVERT

  boxes), or 3 (both inputs true, not used for NULL or INVERT boxes). Then

  type U (reverse the up connection) or D (reverse the down connection).

       After programming the computer you can use C to Compute. This will

  recalculated each box in turn and write a number at the top of each column.

  The number is the output value of the column considered as a binary number

  (but expressed as a decimal number). M will also compute but will play a

  tune, the top three bits set the length of the note (0 for whole note, 1 for

  half, 2 for quarter, and so on). The bottom five bits set the note, 0 is E

  natural in the octave below middle C and each number represents the number

  of half-steps (black or white keys on a piano) above this.

       Here are some other useful keys. SPACE starts the program from the

  initial or help screen. H gets help from the program. E exits the program. F

  saves the current program to a file, L loads from a file. S computes one box

  only. R redraws the screen with no computation. Using any of these keys from

  the help screen gives an explanation.

       There are 4x10^107 different programs that can be written on this

  computer. With some cleverness you can play a simple tune or compute the

  first 12 digits of Pi.