reply

Forms

reply data          # { reply = data; }
reply.right data    # { reply = { right = data; }; }
reply.left  data    # { reply = { left = data; }; }

Description

reply is an attrset with a __functor field, so it works both as a function and as a namespace.

reply data is shorthand for writing { reply = data; } in a behaviour’s return value. The actor extracts reply fields from the state stream to build outbox.

reply.right and reply.left produce Either-tagged values. The outbox stream exposes .right and .left for splitting the stream by tag.

Combining with become

Use // to merge reply and become in one expression:

reply data // become new-beh
# { reply = data; next-behaviour = new-beh; }

Either splitting

validator-c = actor (n:
  if n > 0 then reply.right n
  else reply.left "err: ${toString n}");

a = validator-c { inbox = st 5 (-1) 3; };
a.outbox.toList          # [ { right = 5; } { left = "err: -1"; } { right = 3; } ]
a.outbox.right.toList    # [ 5 3 ]
a.outbox.left.toList     # [ "err: -1" ]

Notes

reply without .right/.left puts the raw value in outbox — no tagging.
A behaviour that returns { } (no reply field) produces no outbox entry for that message.
The reply field can be a ST — states.fields "reply" flattens it, so one message can produce multiple outbox entries.

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