Tagged data (Box)

Almost every plgg value is a Box — a tag plus a content payload:

export type Box<TAG extends string, CONTENT> = Readonly<{
  __tag: TAG;
  content: CONTENT;
}>;

Ok, Err, Some, and the error types (InvalidError, Defect, …) are all just boxes with a known tag. Because the tag is a string literal in the type, the compiler can tell the variants apart, and match can fold them exhaustively.

Build one with the curried box:

import { box } from "plgg";

const notFound = box("NotFound")("/missing");
// { __tag: "NotFound", content: "/missing" }

A variant with no payload (like None) is an Icon — a tag on its own. Together, Box and Icon give plgg tagged unions that are plain, serializable data: no classes, no instanceof, no hidden prototype.

This matters for the rest of the ethos:

• Errors are boxes, not Error subclasses — see Result, not throw.
• Pattern matching is by tag — see Exhaustive match, where pattern("NotFound")() matches the box above.