019 reject destructure unused field

// Destructured fields are bindings: each named field must be USED or be
// spelled `_` — KORU100 per field, the same linear discipline as any
// binding. `age` is named but never read.
~import std/io

~pub tor fetch {} -> { name: []const u8, age: i64 }

~proc fetch|zig { return .{ .name = "lars", .age = 44 }; }

~fetch(): { name, age } |> std/io:print.ln("only {{ name:s }}")