fn takeExprBlock(r: *std.Io.Reader, len: usize) error
fn takeExprBlock(r: *std.Io.Reader, len: usize) error{ ReadFailed, InvalidOperand }![]const u8 { return r.take(len) catch |err| switch (err) { error.ReadFailed => |e| return e, error.EndOfStream => return error.InvalidOperand, }; }