Vog

Vog code moves through one result shape: Ok or Ng.

Ng stands for “no good” — pronounced “N-G,” or “nog” as one syllable. It is a visible, typed failure value, not an exception hiding offscreen. It combines absence, (Maybe types) and error (Result types) into a single shape. Ok is the happy path, and Ng is the many ways you may stray from that path.

01 Division that can't crash

average.vog

pure average(total: Int, count: Int) -> Ok(Int) | Ng(:no_items)
    total
        |> divide(count)
        |> case {
            Ok(n)         -> Ok(n)
            Ng(:div_zero) -> Ng(:no_items)
        }
end

Division returns a result instead of crashing. The signature promises either Ok(Int) or Ng(:no_items), and the handler translates divide-by-zero into the domain error the caller understands.

02 Failure moves through the pipe

profile.vog

flex profile_label(id: Int) -> Ok(String) | Ng(:forbidden)
    id
        |> find_user()
        |> on {             Ng(:none) -> Ok(guest_user())
        }
        |> label_for()
        |> case {
            Ok(label)             -> Ok(label)
            Ng(:forbidden) as err -> err
        }
end

A Ng skips the ordinary stages until a handler catches it; the final case must cover what remains. Unhandled errors don’t slip through unnoticed — they won’t compile.

03 Red, green, red

clamp_low.vog

RED · TEST WRITTEN FIRST

pure clamp_low(x: Int, floor: Int) -> Ok(Int)
    unimplemented
end

assay clamp_low(x: Int, floor: Int) -> Ok(Int)
    clamp_low(x, floor: floor)
end

testrows clamp_low "floor is enforced"
    pending below_floor: 1, floor: 7 -> Ok(7)
end

GREEN · IMPLEMENTATION LANDS

pure clamp_low(x: Int, floor: Int) -> Ok(Int)
    Ok(max(x, floor))
end

testrows clamp_low "floor is enforced"
    pass below_floor: 1, floor: 7 -> Ok(7)
    pass above_floor: 9, floor: 7 -> Ok(9)
end

pending is the red state — the test exists before the function does. Promote it to pass when the code goes green. Then vog invert flips decisions like max → min and checks that a green test actually goes red again. No toothless green.

Real syntax. A taste, on purpose.