emacs/runtime/macros/urm

This is another proof that Vim is perfectly compatible with Vi.
The URM macro package was written by Rudolf Koenig ("Rudi")
(rudolf@koeniglich.de) for hpux-vi in August 1991.

Getting started:

type
in your shell: vim urm
in vim: :so urm.vim
in vim: * (to load the registers and boot the URM-machine :-)
in vim: g (for 'go') and watch the fun. Per default, 3 and 4
are multiplied. Watch the Program counter, it is
visible as a komma moving around.

This is a "standard URM" (Universal register machine) interpreter. The URM
concept is used in theoretical computer science to aid in theorem proving.
Here it proves that vim is a general problem solver (if you bring enough
patience).

The interpreter begins with register 1 (not 0), without macros and more-lines
capability. A dot marks the end of a program. (Bug: there must be a space
after the dot.)

The registers are the first few lines, beginning with a '>' .
The program is the first line after the registers.
You should always initialize the registers required by the program.

Output register: line 2
Input registers: line 2 to ...

Commands:
a increment register
s decrement register
; execute command and then
() execute command while register is nonzero
. ("dot blank") halt the machine.

Examples:

Add register 2 to register 3:
(a2;s3)3.
Multiply register 2 with register 3:
(a4;a5;s2)2; ((a2;s4)4; s3; (a1;a4;s5)5; (a5;s1)1)3.

There are more (complicated) examples in the file examples.
Note, undo may take a while after a division.