data log

use std.obs { log }

fn main() io {
  let id = 42
  log.info("order {id} paid")
  print("logged")
}

logged

use std.obs { log, Level, metric, span }

fn handle(id: i64) -> i64  io {
  log.info("handling request {id}")  // записи идут в stderr, не в stdout
  id * 2
}

fn main() io {
  log.setLevel(Level.Info)
  let served = metric.counter("requests_total", "requests served")
  let inflight = metric.gauge("inflight", "requests in flight")
  var total = 0
  for id in 1..=3 {
    inflight.inc()
    total += span.with("handle", () => handle(id))  // span измеряет участок и попадает в трассу
    served.inc()
    inflight.dec()
  }
  log.debug("not printed: level is Info")
  print("total {total}, served {served.value()}, in flight {inflight.value()}")
  print("debug enabled: {log.enabled(Level.Debug)}")
}

total 12, served 3.0, in flight 0.0
debug enabled: false