ww/lib/io/empty.ww

// ref/hare/io/empty.ha:4-17.
//
// Hare uses `const _empty_vt: vtable = { ... }` + `const empty: *stream`.
// ww can't const-init a vtable struct with fn-ptr fields (#118), so the
// vtable is a module-level `let` and [[empty]] is a function that wires
// the fn-ptr slots on every call and returns the stream pointer.
// Single-assignment on the same words: idempotent under re-entry.
// Lives in empty.ww (not io.ww) so io.ww stays standalone without
// referencing the cross-file vtable/reader/writer types.

package io;

fn _empty_read(s: stream, buf: []u8) (size | eof | error) = {
	let e: eof;
	return e;
};

fn _empty_write(s: stream, buf: []u8) (size | error) = {
	return buf.len: size;
};

let _empty_vt: vtable;

// empty — a stream that discards all writes (returning their size) and
// returns EOF on every read. Mirrors ref/hare/io/empty.ha:13.
// #118: const vtable init with fn-ptr fields is unwired (emit_struct_data
// needs a two-pass reloc extension, node_fnptr_sym reusable). Using a
// mutable let + per-call wiring until #118 lands.
export fn empty() stream = {
	_empty_vt.reader = (&_empty_read): *reader;
	_empty_vt.writer = (&_empty_write): *writer;
	return &_empty_vt;
};