// stream — Hare-shaped vtable surface. Project #94 fold-eFinal.
//
// The single io stream surface (the fold-eFinal collapse retired the
// pre-vtable `stream` struct + `closed` tag). Three exports:
//
//   vtable     a struct of optional fn-pointer slots — reader/writer/
//              closer per ref/hare/io/stream.ha:36-42. Hare spells the
//              nullable as `nullable *T`; ww parser rejects that
//              spelling (#192), so each slot is a `(*T | void)` tagged
//              union (Plan-9-lean per the Nullable kept ruling; opt-in
//              at optionality boundaries only).
//   stream     `*vtable` alias matching Hare's `stream = *vtable`
//              (ref/hare/io/stream.ha:33).
//   read /
//   write /
//   close      the three dispatchers per ref/hare/io/stream.ha:44-68.
//              Each `match`es the matching vtable slot, returns
//              `errors.unsupported` (widened twice) when the slot is
//              void, otherwise calls through the fn pointer. Hare keeps
//              these private (`st_read` …) behind a `handle`-typed
//              public `read`/`write`/`close`; ww has no `handle` yet
//              (io fold-2, #5), so the dispatchers ARE the public
//              surface and grow the `handle` match when #5 lands.
//
// Deferrals (drew-signed): `seeker` lands with io fold-2 (#5) once `off`
// + `whence` plug into the signature. Hare's `?`-propagating `close`
// body (`c(s)?;`) collapses to a direct `return (*c)(s);` here because
// the dispatcher's surface stays Hare-shaped; only the internal
// try-prop is omitted (#173 history, now closed — kept direct for the
// void-arm fall-through shape).

package io;

// ref/hare/io/stream.ha:36-42. Nullable spelling per #192 (ww parser
// rejects `nullable *T`); each slot is `(*T | void)`.
export type vtable = struct {
	reader: (*reader | void),
	writer: (*writer | void),
	closer: (*closer | void),
};

// ref/hare/io/stream.ha:33.
export type stream = *vtable;

// ref/hare/io/stream.ha:44-50. The void-arm `return e;` chains two
// direct widens: `errors.unsupported → error` via #199 α, then
// `error → (size | eof | error)` via #205. The call-arm spells the
// fn-ptr call explicitly per #193 (ww requires `(*r)(args)` rather
// than implicit `r(args)`).
export fn read(s: stream, buf: []u8) (size | eof | error) = {
	match (s.reader) {
	case void => {
		let u: errors.unsupported;
		let e: error = u;
		return e;
	};
	case let r: *reader => return (*r)(s, buf);
	};
};

// ref/hare/io/stream.ha:53-59.
export fn write(s: stream, buf: []u8) (size | error) = {
	match (s.writer) {
	case void => {
		let u: errors.unsupported;
		let e: error = u;
		return e;
	};
	case let w: *writer => return (*w)(s, buf);
	};
};

// ref/hare/io/stream.ha:62-68. Hare propagates the close error via
// `c(s)?;` then falls through to the void arm; ww collapses to a
// direct return for the void-arm fall-through shape. The surface
// (void | error) matches.
export fn close(s: stream) (void | error) = {
	match (s.closer) {
	case void => return void;
	case let c: *closer => return (*c)(s);
	};
};