retro-nga

'no'.

    0  nop      7  jump      14  gt        21  and     28  iquery
    1  lit <v>  8  call      15  fetch     22  or      29  iinteract
    2  dup      9  ccall     16  store     23  xor
    3  drop    10  return    17  add       24  shift
    4  swap    11  eq        18  sub       25  zret
    5  push    12  neq       19  mul       26  end
    6  pop     13  lt        20  divmod    27  ienum

E.g., for a sequence of dup, multiply, no-op, drop:

    i dupmu..dr

An example of a small program:

  if (strcmp(s, "ne") == 0) return 12; if (strcmp(s, "lt") == 0) return 13;
  if (strcmp(s, "gt") == 0) return 14; if (strcmp(s, "fe") == 0) return 15;
  if (strcmp(s, "st") == 0) return 16; if (strcmp(s, "ad") == 0) return 17;
  if (strcmp(s, "su") == 0) return 18; if (strcmp(s, "mu") == 0) return 19;
  if (strcmp(s, "di") == 0) return 20; if (strcmp(s, "an") == 0) return 21;
  if (strcmp(s, "or") == 0) return 22; if (strcmp(s, "xo") == 0) return 23;
  if (strcmp(s, "sh") == 0) return 24; if (strcmp(s, "zr") == 0) return 25;
  if (strcmp(s, "en") == 0) return 26; if (strcmp(s, "ie") == 0) return 27;
  if (strcmp(s, "iq") == 0) return 28; if (strcmp(s, "ii") == 0) return 29;
  return 0;
}
~~~

Now for the first pass. This lays down code, with dummy values
for the references. They will be resolved in `pass2()`.

| 19     | mu   | multiplication     | xy-n       |   -           |
| 20     | di   | divide & remainder | xy-rq      |   -           |
| 21     | an   | bitwise and        | xy-n       |   -           |
| 22     | or   | bitwise or         | xy-n       |   -           |
| 23     | xo   | bitwise xor        | xy-n       |   -           |
| 24     | sh   | shift              | xy-n       |   -           |
| 25     | zr   | zero return        |  n-?       |   -           |
| 26     | en   | end                |   -        |   -           |
| 27     | ie   | i/o enumerate      |   -n       |   -           |
| 28     | iq   | i/o query          |  n-xy      |   -           |
| 29     | ii   | i/o invoke         | ...n-      |   -           |

## Encoding

Up to four instructions can be packed into each memory cell.

| 0008 | Syscalls: Unix   |                            |
| 0009 | Scripting Hooks  |                            |
| 0010 | Random Number    |                            |

This list may be revised in the future. The only guaranteed
stable indentifier is 0000 for generic output.

## Trivia

There are 810,000 possible combinations of instructions. Only
73 are used in the implementation of RETRO.

# Internals: Interface Layers

Nga provides a virtual processor and an extensible way of adding
I/O devices, but does not provide any I/O itself. Adding I/O is
the responsability of the *interface layer*.

An interface layer will wrap Nga, providing at least one I/O

| 19     | mu   | multiplication     | xy-n       |   -           |
| 20     | di   | divide & remainder | xy-rq      |   -           |
| 21     | an   | bitwise and        | xy-n       |   -           |
| 22     | or   | bitwise or         | xy-n       |   -           |
| 23     | xo   | bitwise xor        | xy-n       |   -           |
| 24     | sh   | shift              | xy-n       |   -           |
| 25     | zr   | zero return        |  n-?       |   -           |
| 26     | en   | end                |   -        |   -           |
| 27     | ie   | i/o enumerate      |   -n       |   -           |
| 28     | iq   | i/o query          |  n-xy      |   -           |
| 29     | ii   | i/o invoke         | ...n-      |   -           |

## Encoding

Up to four instructions can be packed into each memory cell.

| 0007 | Network: Sockets |                            |
| 0008 | Syscalls: Unix   |                            |
| 0009 | Scripting Hooks  |                            |
| 0010 | Random Number    |                            |

This list may be revised in the future. The only guaranteed
stable indentifier is 0000 for generic output.

## Trivia

There are 810,000 possible combinations of instructions. Only
73 are used in the implementation of RETRO.

:format (s-)
  (ignore_empty_tokens)
  dup s:length n:zero? [ '  s:put drop ] if;

  (tokens_with_prefixes)
  dup fetch
  $: [ 'colon     span ] case
  $( [ 'comment   span ] case
  $' [ 'str       span ] case
  $# [ 'num       span ] case
  $. [ 'fnum      span ] case
  $& [ 'ptr       span ] case
  $$ [ 'char      span ] case
  $` [ 'inst      span ] case
  $\ [ 'inst      span ] case

/* CSS Begins */

* { background: #1d1f21; color: #b5bd68; font-family: monospace; }
span { white-space: pre }
.text { color: #c5c8c6; white-space: pre }
.colon {  color:  #cc6666; }
.comment {  color: #969896; }
.str {  color: #f0c674; }
.num { color: #8abeb7; }
.fnum { color: #8abeb7; font-weight: bold; }
.ptr { color: #b294bb; font-weight: bold; }
.fetch { color: #b294bb; }
.store { color: #b294bb; }
.char { color:  #81a2be; }
.inst { color: #de935f; }
.defer { color: #888; }
.imm { color: #de935f; }
.prim { color: #b5bd68; font-weight: bold; }