World Edge

The world edge

dnzl actors are pure functions. They never read from files, call external services, or produce side effects. The “world edge” is where you connect actors to the outside world — feeding in static data and reading out results.

ned.run

run is the standard entry point. It takes a { inbox } attrset and a cycle-c, runs the cycle, and returns { outbox, states, ... }:

inherit (dnzl.ned) run static-d st when-c;
inherit (dnzl) actor reply become;

counter = count: msg:
  if msg == "inc" then reply.right (count + 1) // become (counter (count + 1))
  else if msg == "get" then reply.right count
  else { };

counter-c = actor (counter 0);

result = run { inbox = static-d [ "inc" "inc" "get" ]; } counter-c;
result.outbox.toList
# [ { right = 1; } { right = 2; } { right = 2; } ]

static-d converts a Nix list to an ST stream. It is the standard way to feed static inputs.

Inline anonymous cycle

run accepts any cycle-c, including an anonymous lambda:

result = run { inbox = static-d [ "inc" "inc" "get" ]; } (
  { inbox }:
  counter-c { inherit inbox; }
);

Useful for one-off wiring without naming the cycle.

Collecting results

result.outbox is a ST. Convert to a Nix list with .toList:

result.outbox.toList          # all replies
result.outbox.right.toList    # successes only
result.outbox.left.toList     # errors only

Access the full state stream for side-channel data:

result.states.fields "log"    # ST of log values from each state
(result.states.fields "log").toList

Composite inline cycle

Wire multiple actors inside run:

result = run {
  inbox = static-d [
    { type = "count"; cmd = "inc"; }
    { type = "count"; cmd = "inc"; }
    { type = "div"; dividend = 10; divisor = 2; }
    { type = "count"; cmd = "get"; }
  ];
} (
  { inbox }:
  let
    counts  = counter-c { inbox = when-c (m: m.type == "count") inbox (m: m.cmd); };
    divides = div-c     { inbox = when-c (m: m.type == "div")   inbox (m: m);     };
  in
  { outbox = counts.outbox (divides.outbox); }
);

result.outbox.toList
# [ { right = 1; } { right = 2; } { right = 2; } { right = 5; } ]

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