// errors — error type (a string) and a few sentinels. Plan 9 model:
// the empty string means OK, a non-empty string is the message.

type error = str;

def eof:        error = "eof";
def underread:  error = "short read";
def underwrite: error = "short write";
def closed:     error = "closed";
def invalid:    error = "invalid argument";
def noaccess:   error = "permission denied";
def noentry:    error = "not found";
def exists:     error = "already exists";

export fn isnil(e: error) bool = {
	return e.len == 0;
};

// equal — compare an error against a sentinel (or any other error).
// Pure byte equality. (Was `errors.is` before `is` became a keyword
// for tagged-union type-tests; rename matches bytes.equal / strings.equal.)
export fn equal(e: error, want: error) bool = {
	if (e.len != want.len) { return false; };
	let i: i32 = 0;
	for (i < e.len) {
		if (e[i] != want[i]) { return false; };
		i += 1;
	};
	return true;
};