datastream/sink

Side-effecting terminal consumers over Stream(a).

sink is the effectful half of the terminal layer; pure reductions live in fold. The split is intentional: a reader can tell from the import whether a function is pure (fold) or effectful (sink).

fold.drain already covers the “evaluate and discard” case, so a sink.drain synonym is intentionally omitted.

Values

each

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pub fn each(
  over stream: datastream.Stream(a),
  with effect: fn(a) -> Nil,
) -> Nil

Drive the stream to completion, calling effect once per element in source order. Returns Nil.

Use this when the work the consumer does is infallible. For fallible consumers use try_each.

println

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pub fn println(stream: datastream.Stream(String)) -> Nil

Print every element of stream followed by a newline to standard output, in source order.

Cross-target convenience over gleam/io.println. Target-aware sinks (file, socket, …) belong outside the cross-target core.

try_each

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pub fn try_each(
  over stream: datastream.Stream(a),
  with effect: fn(a) -> Result(Nil, e),
) -> Result(Nil, e)

Drive the stream while effect returns Ok(Nil), halting on the first Error(e) and returning that error.

On all-Ok returns Ok(Nil). On the first Error(e), no further element is pulled from upstream and the upstream’s close callback is invoked before Error(e) is returned, so resource-backed sources are released even on the early-exit path.