src/lexical/token_queue.ghul

1		namespace Lexical is
2		use Collections;
3
4		use Logging;
5
6		class TOKEN_QUEUE is
7		_buffer: LIST[TOKEN_PAIR];
8		_speculate_index: int;
9		_read_index: int; // points at the last token read
10		_write_index: int; // points at the last token written
11		_size: int;
12
13		count: int => (_write_index - _read_index + _size) & (_size - 1);
14
15		avail: bool => count > 0;
16
17		is_speculating: bool => _speculate_index != -1;
18
19		_peek_offset(index: int) -> int =>
20		(_read_index + index) & (_size - 1);
21
22		_next_index(index: int) -> int =>
23		(index + 1) & (_size - 1);
24
25		_prev_index(index: int) -> int =>
26		(index - 1) & (_size - 1);
27
28		init(size: int) is
29		assert size > 0 else "token queue size must be greater than 0";
30		assert (size & (size - 1)) == 0 else "token queue size must be a power of 2";
31
32		_size = size;
33		_read_index = 0;
34		_write_index = 0;
35		_speculate_index = -1;
36
37		_buffer = LIST[TOKEN_PAIR](_size);
38
39		// .NET can be very annoying sometimes...
40
41		for i in 0.._size do
42		_buffer.add(null);
43		od
44		si
45
46		speculate_enter() is
47		assert _speculate_index == -1 else "already speculating";
48		_speculate_index = _read_index;
49		si
50
51		speculate_exit() is
52		assert _speculate_index != -1 else "not speculating";
53		_speculate_index = -1;
54		si
55
56		get_read_index() -> int => _read_index;
57
58		mark() -> int is
59		assert _speculate_index != -1 else "not speculating";
60
61		return _read_index;
62		si
63
64		release(index: int) is
65		assert _speculate_index != -1 else "not speculating";
66		_read_index = index;
67		si
68
69		last() -> TOKEN_PAIR => _buffer[_read_index];
70
71		enqueue(token: TOKEN_PAIR) is
72		let new_write_index = _next_index(_write_index);
73
74		assert new_write_index != _read_index /\ new_write_index != _speculate_index else "token queue overflow";
75
76		_write_index = new_write_index;
77
78		_buffer[_write_index] = token;
79		si
80
81		dequeue() -> TOKEN_PAIR is
82		assert _read_index != _write_index else "token queue underflow";
83
84		_read_index = _next_index(_read_index);
85
86		let result = _buffer[_read_index];
87
88		return result;
89		si
90		si
91		si