From Go

Go and Khora agree about the shape of the artifact: one native executable, no VM beside it, fast start, and an operational story you can hold in your head. They disagree about how much of a service’s behaviour belongs in the type. Four places where a Go habit needs adjusting, with the Khora each of them becomes.

Errors: the second return value moves into the type

Go returns failure as a value, by convention, and the compiler is happy if you ignore it:

user, err := loadUser(id)
if err != nil {
    return Response{}, err
}

Khora puts the failure channel in the signature. The failure type is an ordinary ADT:

pub type UserError =
  | NotFound(id: Id)
  | Unavailable(reason: String);

and the function says it uses the channel:

fn load_user(id: Id) -> User
  raises UserError
{
  // ...
}

The if err != nil becomes a postfix ! at the call, which propagates:

Id -> User raises UserError

Three consequences a Go reader should expect:

• ! is not ? and it is not panic. It says this call may fail and I am letting the failure out of here, which is only legal if the enclosing function’s own raises row admits it. A missing ! is a compile error, not a dropped error.
• raises composes with + — raises UserError + HttpError — rather than collapsing to one error interface, so the arms of a catch are checked for exhaustiveness the way a match is.
• There is no errors.Is / errors.As unwrapping ceremony, because nothing was wrapped into an interface to begin with. Failures has catch and attempt, which are the two ways back out.

The habit to drop: returning a zero value beside an error. A Khora function that fails does not also produce an answer, so there is no zero Response{} to invent and no caller reading one by mistake.

Dependencies: from a struct field to a with row

Go passes a *sql.DB, a logger and a clock down through constructors, or reaches for a package-level variable. Khora makes the requirement part of the type, and it is discharged once, at the boundary:

with {
  config: env_config(),
  scope: Scope::root(),
  db: postgres_db()!,
  store: sql_store(),
} {
  run_server()!
}

Everything inside that block can call functions declaring with { db: Db } without being handed a db argument, and a function that does not declare it cannot reach one. That is the part with no Go analogue: the absence of ambient authority is checked, so a helper five layers down cannot quietly open a socket.

The habit to drop: the context.Context first parameter. It is carrying three different things — cancellation, deadlines and request-scoped values — and each of them has its own home here. Values are capabilities in the with row. Cancellation belongs to the nursery, below. Deadlines are the piece that does not exist yet: there is no timeout, no race and no select, and Concurrency says so plainly rather than leaving you to find out.

Concurrency: go f() always has an owner

The Go loop that starts work and hopes:

for _, job := range jobs {
    go handle(job)
}

has no answer to who waits for these, what happens when one panics, or what stops them. A sync.WaitGroup and a context are the conventional answers and neither is enforced. In Khora a fiber is adopted by a nursery, and the nursery is a scope that does not return until its children are done:

module main;

import std::core::{ChildFailed, Fiber, Nursery, bounded_nursery, print};

fn handle(job: Int) -> () {
  print("processing job ${job}");
}

fn launch_jobs() -> ()
  with { nursery: Nursery }
{
  let mut next = 0;

  while next < 1000 {
    let job = next;

    nursery.adopt(
      Fiber::spawn(fn () => handle(job))
    );

    next = next + 1;
  }
}

pub fn main() raises ChildFailed {
  bounded_nursery(64, launch_jobs)!
}

bounded_nursery(64, ...) is also the WaitGroup plus the semaphore Go programs write by hand: adoption blocks once the limit is live, so the producer slows at the boundary where it makes work instead of filling a queue. See Bound concurrent work, including the off-by-one to subtract when the limit is a real resource.

Two of those three questions are answered today. Every child is waited for and a failure is always reported as ChildFailed. The first failure is intended to cancel its siblings and does so unreliably — reliably when the failing child was adopted first, and usually not otherwise — so work that is expensive, holds a resource, or has an effect outside the process should check a Shared flag itself rather than expect the group to collapse promptly. The group does collapse and every child is waited for; it is the promptness that is not yet something to build on. Known limitations has the measurements. A Go reader coming off errgroup, where the first error does cancel the group’s context, should not assume the same here.

Cancellation arrives without a ctx.Done() channel to select on, because a cancellation travels out on the same tagged return a failure does. It is observed at a ! and at a loop back-edge, which is what makes an ordinary polling worker stoppable with nothing in it that looks like a cancellation check:

fn reaper() -> () with { clock: Clock } raises Stop {
  loop {
    clock.sleep(1000);
    sweep();
  }
}

The habit to drop: a bare go. There isn’t one — Fiber::spawn produces a handle, and you either join it for its answer or adopt it into a nursery that will.

Memory: reference counting instead of a tracing collector

Go’s collector gives you no annotations and a tail. Khora’s answer is Perceus reference counting with compiler ownership and reuse analysis: also no annotations, no borrow checker, and no collector thread — the counts are inserted at compile time and a uniquely-owned value is reused in place rather than freed and reallocated.

What that changes operationally is the shape of the latency curve and the resident set rather than the code you write. The Performance page has the measured numbers, the ladder they were taken on, and what is explicitly not measured; it is the page to read before quoting anything.

The one place a Go programmer gets less: a reference cycle leaks. A tracing collector is what Khora exists not to have, so there is no cycle collector, and weak references — the usual way to break one — do not exist yet either. A cycle needs a mut field deliberately pointing back at something that already reaches it, so it is not accidental; it is also not caught. The leak is bounded and quiet rather than unsound: nothing is freed early and nothing is read after free, the memory is simply never returned.

What stays familiar

Direct-looking code with no monadic plumbing, one binary to ship, a standard library that covers HTTP and TLS, structured logging as JSON on standard error, and a small number of runtime concepts visible in application code. khora fmt is gofmt’s idea — canonical formatting, not a style argument — and khora test . compiles and runs the package’s tests one fiber each.

The thing that is genuinely missing rather than different: there is no package registry, so a dependency is a git URL, and khora install fetches and locks what khora.toml declares. Modules and packages is the page for that.