~nch/gamelog

ref: 75432213d3972f26c03ef636da68ed482f0ac908 gamelog/fun.lua -rw-r--r-- 28.3 KiB View raw
75432213 — nc refactoring debug code out a bit 5 months ago
                                                                                
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
---
--- Lua Fun - a high-performance functional programming library for LuaJIT
---
--- Copyright (c) 2013-2017 Roman Tsisyk <roman@tsisyk.com>
---
--- Distributed under the MIT/X11 License. See COPYING.md for more details.
---

local exports = {}
local methods = {}

-- compatibility with Lua 5.1/5.2
local unpack = rawget(table, "unpack") or unpack

--------------------------------------------------------------------------------
-- Tools
--------------------------------------------------------------------------------

local return_if_not_empty = function(state_x, ...)
    if state_x == nil then
        return nil
    end
    return ...
end

local call_if_not_empty = function(fun, state_x, ...)
    if state_x == nil then
        return nil
    end
    return state_x, fun(...)
end

local function deepcopy(orig) -- used by cycle()
    local orig_type = type(orig)
    local copy
    if orig_type == 'table' then
        copy = {}
        for orig_key, orig_value in next, orig, nil do
            copy[deepcopy(orig_key)] = deepcopy(orig_value)
        end
    else
        copy = orig
    end
    return copy
end

local iterator_mt = {
    -- usually called by for-in loop
    __call = function(self, param, state)
        return self.gen(param, state)
    end;
    __tostring = function(self)
        return '<generator>'
    end;
    -- add all exported methods
    __index = methods;
}

local wrap = function(gen, param, state)
    return setmetatable({
        gen = gen,
        param = param,
        state = state
    }, iterator_mt), param, state
end
exports.wrap = wrap

local unwrap = function(self)
    return self.gen, self.param, self.state
end
methods.unwrap = unwrap

--------------------------------------------------------------------------------
-- Basic Functions
--------------------------------------------------------------------------------

local nil_gen = function(_param, _state)
    return nil
end

local string_gen = function(param, state)
    local state = state + 1
    if state > #param then
        return nil
    end
    local r = string.sub(param, state, state)
    return state, r
end

local ipairs_gen = ipairs({}) -- get the generating function from ipairs

local pairs_gen = pairs({ a = 0 }) -- get the generating function from pairs
local map_gen = function(tab, key)
    local value
    local key, value = pairs_gen(tab, key)
    return key, key, value
end

local rawiter = function(obj, param, state)
    assert(obj ~= nil, "invalid iterator")
    if type(obj) == "table" then
        local mt = getmetatable(obj);
        if mt ~= nil then
            if mt == iterator_mt then
                return obj.gen, obj.param, obj.state
            elseif mt.__ipairs ~= nil then
                return mt.__ipairs(obj)
            elseif mt.__pairs ~= nil then
                return mt.__pairs(obj)
            end
        end
        if #obj > 0 then
            -- array
            return ipairs(obj)
        else
            -- hash
            return map_gen, obj, nil
        end
    elseif (type(obj) == "function") then
        return obj, param, state
    elseif (type(obj) == "string") then
        if #obj == 0 then
            return nil_gen, nil, nil
        end
        return string_gen, obj, 0
    end
    error(string.format('object %s of type "%s" is not iterable',
          obj, type(obj)))
end

local iter = function(obj, param, state)
    return wrap(rawiter(obj, param, state))
end
exports.iter = iter

local method0 = function(fun)
    return function(self)
        return fun(self.gen, self.param, self.state)
    end
end

local method1 = function(fun)
    return function(self, arg1)
        return fun(arg1, self.gen, self.param, self.state)
    end
end

local method2 = function(fun)
    return function(self, arg1, arg2)
        return fun(arg1, arg2, self.gen, self.param, self.state)
    end
end

local export0 = function(fun)
    return function(gen, param, state)
        return fun(rawiter(gen, param, state))
    end
end

local export1 = function(fun)
    return function(arg1, gen, param, state)
        return fun(arg1, rawiter(gen, param, state))
    end
end

local export2 = function(fun)
    return function(arg1, arg2, gen, param, state)
        return fun(arg1, arg2, rawiter(gen, param, state))
    end
end

local each = function(fun, gen, param, state)
    repeat
        state = call_if_not_empty(fun, gen(param, state))
    until state == nil
end
methods.each = method1(each)
exports.each = export1(each)
methods.for_each = methods.each
exports.for_each = exports.each
methods.foreach = methods.each
exports.foreach = exports.each

--------------------------------------------------------------------------------
-- Generators
--------------------------------------------------------------------------------

local range_gen = function(param, state)
    local stop, step = param[1], param[2]
    local state = state + step
    if state > stop then
        return nil
    end
    return state, state
end

local range_rev_gen = function(param, state)
    local stop, step = param[1], param[2]
    local state = state + step
    if state < stop then
        return nil
    end
    return state, state
end

local range = function(start, stop, step)
    if step == nil then
        if stop == nil then
            if start == 0 then
                return nil_gen, nil, nil
            end
            stop = start
            start = stop > 0 and 1 or -1
        end
        step = start <= stop and 1 or -1
    end

    assert(type(start) == "number", "start must be a number")
    assert(type(stop) == "number", "stop must be a number")
    assert(type(step) == "number", "step must be a number")
    assert(step ~= 0, "step must not be zero")

    if (step > 0) then
        return wrap(range_gen, {stop, step}, start - step)
    elseif (step < 0) then
        return wrap(range_rev_gen, {stop, step}, start - step)
    end
end
exports.range = range

local duplicate_table_gen = function(param_x, state_x)
    return state_x + 1, unpack(param_x)
end

local duplicate_fun_gen = function(param_x, state_x)
    return state_x + 1, param_x(state_x)
end

local duplicate_gen = function(param_x, state_x)
    return state_x + 1, param_x
end

local duplicate = function(...)
    if select('#', ...) <= 1 then
        return wrap(duplicate_gen, select(1, ...), 0)
    else
        return wrap(duplicate_table_gen, {...}, 0)
    end
end
exports.duplicate = duplicate
exports.replicate = duplicate
exports.xrepeat = duplicate

local tabulate = function(fun)
    assert(type(fun) == "function")
    return wrap(duplicate_fun_gen, fun, 0)
end
exports.tabulate = tabulate

local zeros = function()
    return wrap(duplicate_gen, 0, 0)
end
exports.zeros = zeros

local ones = function()
    return wrap(duplicate_gen, 1, 0)
end
exports.ones = ones

local rands_gen = function(param_x, _state_x)
    return 0, math.random(param_x[1], param_x[2])
end

local rands_nil_gen = function(_param_x, _state_x)
    return 0, math.random()
end

local rands = function(n, m)
    if n == nil and m == nil then
        return wrap(rands_nil_gen, 0, 0)
    end
    assert(type(n) == "number", "invalid first arg to rands")
    if m == nil then
        m = n
        n = 0
    else
        assert(type(m) == "number", "invalid second arg to rands")
    end
    assert(n < m, "empty interval")
    return wrap(rands_gen, {n, m - 1}, 0)
end
exports.rands = rands

--------------------------------------------------------------------------------
-- Slicing
--------------------------------------------------------------------------------

local nth = function(n, gen_x, param_x, state_x)
    assert(n > 0, "invalid first argument to nth")
    -- An optimization for arrays and strings
    if gen_x == ipairs_gen then
        return param_x[n]
    elseif gen_x == string_gen then
        if n <= #param_x then
            return string.sub(param_x, n, n)
        else
            return nil
        end
    end
    for i=1,n-1,1 do
        state_x = gen_x(param_x, state_x)
        if state_x == nil then
            return nil
        end
    end
    return return_if_not_empty(gen_x(param_x, state_x))
end
methods.nth = method1(nth)
exports.nth = export1(nth)

local head_call = function(state, ...)
    if state == nil then
        error("head: iterator is empty")
    end
    return ...
end

local head = function(gen, param, state)
    return head_call(gen(param, state))
end
methods.head = method0(head)
exports.head = export0(head)
exports.car = exports.head
methods.car = methods.head

local tail = function(gen, param, state)
    state = gen(param, state)
    if state == nil then
        return wrap(nil_gen, nil, nil)
    end
    return wrap(gen, param, state)
end
methods.tail = method0(tail)
exports.tail = export0(tail)
exports.cdr = exports.tail
methods.cdr = methods.tail

local take_n_gen_x = function(i, state_x, ...)
    if state_x == nil then
        return nil
    end
    return {i, state_x}, ...
end

local take_n_gen = function(param, state)
    local n, gen_x, param_x = param[1], param[2], param[3]
    local i, state_x = state[1], state[2]
    if i >= n then
        return nil
    end
    return take_n_gen_x(i + 1, gen_x(param_x, state_x))
end

local take_n = function(n, gen, param, state)
    assert(n >= 0, "invalid first argument to take_n")
    return wrap(take_n_gen, {n, gen, param}, {0, state})
end
methods.take_n = method1(take_n)
exports.take_n = export1(take_n)

local take_while_gen_x = function(fun, state_x, ...)
    if state_x == nil or not fun(...) then
        return nil
    end
    return state_x, ...
end

local take_while_gen = function(param, state_x)
    local fun, gen_x, param_x = param[1], param[2], param[3]
    return take_while_gen_x(fun, gen_x(param_x, state_x))
end

local take_while = function(fun, gen, param, state)
    assert(type(fun) == "function", "invalid first argument to take_while")
    return wrap(take_while_gen, {fun, gen, param}, state)
end
methods.take_while = method1(take_while)
exports.take_while = export1(take_while)

local take = function(n_or_fun, gen, param, state)
    if type(n_or_fun) == "number" then
        return take_n(n_or_fun, gen, param, state)
    else
        return take_while(n_or_fun, gen, param, state)
    end
end
methods.take = method1(take)
exports.take = export1(take)

local drop_n = function(n, gen, param, state)
    assert(n >= 0, "invalid first argument to drop_n")
    local i
    for i=1,n,1 do
        state = gen(param, state)
        if state == nil then
            return wrap(nil_gen, nil, nil)
        end
    end
    return wrap(gen, param, state)
end
methods.drop_n = method1(drop_n)
exports.drop_n = export1(drop_n)

local drop_while_x = function(fun, state_x, ...)
    if state_x == nil or not fun(...) then
        return state_x, false
    end
    return state_x, true, ...
end

local drop_while = function(fun, gen_x, param_x, state_x)
    assert(type(fun) == "function", "invalid first argument to drop_while")
    local cont, state_x_prev
    repeat
        state_x_prev = deepcopy(state_x)
        state_x, cont = drop_while_x(fun, gen_x(param_x, state_x))
    until not cont
    if state_x == nil then
        return wrap(nil_gen, nil, nil)
    end
    return wrap(gen_x, param_x, state_x_prev)
end
methods.drop_while = method1(drop_while)
exports.drop_while = export1(drop_while)

local drop = function(n_or_fun, gen_x, param_x, state_x)
    if type(n_or_fun) == "number" then
        return drop_n(n_or_fun, gen_x, param_x, state_x)
    else
        return drop_while(n_or_fun, gen_x, param_x, state_x)
    end
end
methods.drop = method1(drop)
exports.drop = export1(drop)

local split = function(n_or_fun, gen_x, param_x, state_x)
    return take(n_or_fun, gen_x, param_x, state_x),
           drop(n_or_fun, gen_x, param_x, state_x)
end
methods.split = method1(split)
exports.split = export1(split)
methods.split_at = methods.split
exports.split_at = exports.split
methods.span = methods.split
exports.span = exports.split

--------------------------------------------------------------------------------
-- Indexing
--------------------------------------------------------------------------------

local index = function(x, gen, param, state)
    local i = 1
    for _k, r in gen, param, state do
        if r == x then
            return i
        end
        i = i + 1
    end
    return nil
end
methods.index = method1(index)
exports.index = export1(index)
methods.index_of = methods.index
exports.index_of = exports.index
methods.elem_index = methods.index
exports.elem_index = exports.index

local indexes_gen = function(param, state)
    local x, gen_x, param_x = param[1], param[2], param[3]
    local i, state_x = state[1], state[2]
    local r
    while true do
        state_x, r = gen_x(param_x, state_x)
        if state_x == nil then
            return nil
        end
        i = i + 1
        if r == x then
            return {i, state_x}, i
        end
    end
end

local indexes = function(x, gen, param, state)
    return wrap(indexes_gen, {x, gen, param}, {0, state})
end
methods.indexes = method1(indexes)
exports.indexes = export1(indexes)
methods.elem_indexes = methods.indexes
exports.elem_indexes = exports.indexes
methods.indices = methods.indexes
exports.indices = exports.indexes
methods.elem_indices = methods.indexes
exports.elem_indices = exports.indexes

--------------------------------------------------------------------------------
-- Filtering
--------------------------------------------------------------------------------

local filter1_gen = function(fun, gen_x, param_x, state_x, a)
    while true do
        if state_x == nil or fun(a) then break; end
        state_x, a = gen_x(param_x, state_x)
    end
    return state_x, a
end

-- call each other
local filterm_gen
local filterm_gen_shrink = function(fun, gen_x, param_x, state_x)
    return filterm_gen(fun, gen_x, param_x, gen_x(param_x, state_x))
end

filterm_gen = function(fun, gen_x, param_x, state_x, ...)
    if state_x == nil then
        return nil
    end
    if fun(...) then
        return state_x, ...
    end
    return filterm_gen_shrink(fun, gen_x, param_x, state_x)
end

local filter_detect = function(fun, gen_x, param_x, state_x, ...)
    if select('#', ...) < 2 then
        return filter1_gen(fun, gen_x, param_x, state_x, ...)
    else
        return filterm_gen(fun, gen_x, param_x, state_x, ...)
    end
end

local filter_gen = function(param, state_x)
    local fun, gen_x, param_x = param[1], param[2], param[3]
    return filter_detect(fun, gen_x, param_x, gen_x(param_x, state_x))
end

local filter = function(fun, gen, param, state)
    return wrap(filter_gen, {fun, gen, param}, state)
end
methods.filter = method1(filter)
exports.filter = export1(filter)
methods.remove_if = methods.filter
exports.remove_if = exports.filter

local grep = function(fun_or_regexp, gen, param, state)
    local fun = fun_or_regexp
    if type(fun_or_regexp) == "string" then
        fun = function(x) return string.find(x, fun_or_regexp) ~= nil end
    end
    return filter(fun, gen, param, state)
end
methods.grep = method1(grep)
exports.grep = export1(grep)

local partition = function(fun, gen, param, state)
    local neg_fun = function(...)
        return not fun(...)
    end
    return filter(fun, gen, param, state),
           filter(neg_fun, gen, param, state)
end
methods.partition = method1(partition)
exports.partition = export1(partition)

--------------------------------------------------------------------------------
-- Reducing
--------------------------------------------------------------------------------

local foldl_call = function(fun, start, state, ...)
    if state == nil then
        return nil, start
    end
    return state, fun(start, ...)
end

local foldl = function(fun, start, gen_x, param_x, state_x)
    while true do
        state_x, start = foldl_call(fun, start, gen_x(param_x, state_x))
        if state_x == nil then
            break;
        end
    end
    return start
end
methods.foldl = method2(foldl)
exports.foldl = export2(foldl)
methods.reduce = methods.foldl
exports.reduce = exports.foldl

local length = function(gen, param, state)
    if gen == ipairs_gen or gen == string_gen then
        return #param
    end
    local len = 0
    repeat
        state = gen(param, state)
        len = len + 1
    until state == nil
    return len - 1
end
methods.length = method0(length)
exports.length = export0(length)

local is_null = function(gen, param, state)
    return gen(param, deepcopy(state)) == nil
end
methods.is_null = method0(is_null)
exports.is_null = export0(is_null)

local is_prefix_of = function(iter_x, iter_y)
    local gen_x, param_x, state_x = iter(iter_x)
    local gen_y, param_y, state_y = iter(iter_y)

    local r_x, r_y
    for i=1,10,1 do
        state_x, r_x = gen_x(param_x, state_x)
        state_y, r_y = gen_y(param_y, state_y)
        if state_x == nil then
            return true
        end
        if state_y == nil or r_x ~= r_y then
            return false
        end
    end
end
methods.is_prefix_of = is_prefix_of
exports.is_prefix_of = is_prefix_of

local all = function(fun, gen_x, param_x, state_x)
    local r
    repeat
        state_x, r = call_if_not_empty(fun, gen_x(param_x, state_x))
    until state_x == nil or not r
    return state_x == nil
end
methods.all = method1(all)
exports.all = export1(all)
methods.every = methods.all
exports.every = exports.all

local any = function(fun, gen_x, param_x, state_x)
    local r
    repeat
        state_x, r = call_if_not_empty(fun, gen_x(param_x, state_x))
    until state_x == nil or r
    return not not r
end
methods.any = method1(any)
exports.any = export1(any)
methods.some = methods.any
exports.some = exports.any

local sum = function(gen, param, state)
    local s = 0
    local r = 0
    repeat
        s = s + r
        state, r = gen(param, state)
    until state == nil
    return s
end
methods.sum = method0(sum)
exports.sum = export0(sum)

local product = function(gen, param, state)
    local p = 1
    local r = 1
    repeat
        p = p * r
        state, r = gen(param, state)
    until state == nil
    return p
end
methods.product = method0(product)
exports.product = export0(product)

local min_cmp = function(m, n)
    if n < m then return n else return m end
end

local max_cmp = function(m, n)
    if n > m then return n else return m end
end

local min = function(gen, param, state)
    local state, m = gen(param, state)
    if state == nil then
        error("min: iterator is empty")
    end

    local cmp
    if type(m) == "number" then
        -- An optimization: use math.min for numbers
        cmp = math.min
    else
        cmp = min_cmp
    end

    for _, r in gen, param, state do
        m = cmp(m, r)
    end
    return m
end
methods.min = method0(min)
exports.min = export0(min)
methods.minimum = methods.min
exports.minimum = exports.min

local min_by = function(cmp, gen_x, param_x, state_x)
    local state_x, m = gen_x(param_x, state_x)
    if state_x == nil then
        error("min: iterator is empty")
    end

    for _, r in gen_x, param_x, state_x do
        m = cmp(m, r)
    end
    return m
end
methods.min_by = method1(min_by)
exports.min_by = export1(min_by)
methods.minimum_by = methods.min_by
exports.minimum_by = exports.min_by

local max = function(gen_x, param_x, state_x)
    local state_x, m = gen_x(param_x, state_x)
    if state_x == nil then
        error("max: iterator is empty")
    end

    local cmp
    if type(m) == "number" then
        -- An optimization: use math.max for numbers
        cmp = math.max
    else
        cmp = max_cmp
    end

    for _, r in gen_x, param_x, state_x do
        m = cmp(m, r)
    end
    return m
end
methods.max = method0(max)
exports.max = export0(max)
methods.maximum = methods.max
exports.maximum = exports.max

local max_by = function(cmp, gen_x, param_x, state_x)
    local state_x, m = gen_x(param_x, state_x)
    if state_x == nil then
        error("max: iterator is empty")
    end

    for _, r in gen_x, param_x, state_x do
        m = cmp(m, r)
    end
    return m
end
methods.max_by = method1(max_by)
exports.max_by = export1(max_by)
methods.maximum_by = methods.maximum_by
exports.maximum_by = exports.maximum_by

local totable = function(gen_x, param_x, state_x)
    local tab, key, val = {}
    while true do
        state_x, val = gen_x(param_x, state_x)
        if state_x == nil then
            break
        end
        table.insert(tab, val)
    end
    return tab
end
methods.totable = method0(totable)
exports.totable = export0(totable)

local tomap = function(gen_x, param_x, state_x)
    local tab, key, val = {}
    while true do
        state_x, key, val = gen_x(param_x, state_x)
        if state_x == nil then
            break
        end
        tab[key] = val
    end
    return tab
end
methods.tomap = method0(tomap)
exports.tomap = export0(tomap)

--------------------------------------------------------------------------------
-- Transformations
--------------------------------------------------------------------------------

local map_gen = function(param, state)
    local gen_x, param_x, fun = param[1], param[2], param[3]
    return call_if_not_empty(fun, gen_x(param_x, state))
end

local map = function(fun, gen, param, state)
    return wrap(map_gen, {gen, param, fun}, state)
end
methods.map = method1(map)
exports.map = export1(map)

local enumerate_gen_call = function(state, i, state_x, ...)
    if state_x == nil then
        return nil
    end
    return {i + 1, state_x}, i, ...
end

local enumerate_gen = function(param, state)
    local gen_x, param_x = param[1], param[2]
    local i, state_x = state[1], state[2]
    return enumerate_gen_call(state, i, gen_x(param_x, state_x))
end

local enumerate = function(gen, param, state)
    return wrap(enumerate_gen, {gen, param}, {1, state})
end
methods.enumerate = method0(enumerate)
exports.enumerate = export0(enumerate)

local intersperse_call = function(i, state_x, ...)
    if state_x == nil then
        return nil
    end
    return {i + 1, state_x}, ...
end

local intersperse_gen = function(param, state)
    local x, gen_x, param_x = param[1], param[2], param[3]
    local i, state_x = state[1], state[2]
    if i % 2 == 1 then
        return {i + 1, state_x}, x
    else
        return intersperse_call(i, gen_x(param_x, state_x))
    end
end

-- TODO: interperse must not add x to the tail
local intersperse = function(x, gen, param, state)
    return wrap(intersperse_gen, {x, gen, param}, {0, state})
end
methods.intersperse = method1(intersperse)
exports.intersperse = export1(intersperse)

--------------------------------------------------------------------------------
-- Compositions
--------------------------------------------------------------------------------

local function zip_gen_r(param, state, state_new, ...)
    if #state_new == #param / 2 then
        return state_new, ...
    end

    local i = #state_new + 1
    local gen_x, param_x = param[2 * i - 1], param[2 * i]
    local state_x, r = gen_x(param_x, state[i])
    if state_x == nil then
        return nil
    end
    table.insert(state_new, state_x)
    return zip_gen_r(param, state, state_new, r, ...)
end

local zip_gen = function(param, state)
    return zip_gen_r(param, state, {})
end

-- A special hack for zip/chain to skip last two state, if a wrapped iterator
-- has been passed
local numargs = function(...)
    local n = select('#', ...)
    if n >= 3 then
        -- Fix last argument
        local it = select(n - 2, ...)
        if type(it) == 'table' and getmetatable(it) == iterator_mt and
           it.param == select(n - 1, ...) and it.state == select(n, ...) then
            return n - 2
        end
    end
    return n
end

local zip = function(...)
    local n = numargs(...)
    if n == 0 then
        return wrap(nil_gen, nil, nil)
    end
    local param = { [2 * n] = 0 }
    local state = { [n] = 0 }

    local i, gen_x, param_x, state_x
    for i=1,n,1 do
        local it = select(n - i + 1, ...)
        gen_x, param_x, state_x = rawiter(it)
        param[2 * i - 1] = gen_x
        param[2 * i] = param_x
        state[i] = state_x
    end

    return wrap(zip_gen, param, state)
end
methods.zip = zip
exports.zip = zip

local cycle_gen_call = function(param, state_x, ...)
    if state_x == nil then
        local gen_x, param_x, state_x0 = param[1], param[2], param[3]
        return gen_x(param_x, deepcopy(state_x0))
    end
    return state_x, ...
end

local cycle_gen = function(param, state_x)
    local gen_x, param_x, state_x0 = param[1], param[2], param[3]
    return cycle_gen_call(param, gen_x(param_x, state_x))
end

local cycle = function(gen, param, state)
    return wrap(cycle_gen, {gen, param, state}, deepcopy(state))
end
methods.cycle = method0(cycle)
exports.cycle = export0(cycle)

-- call each other
local chain_gen_r1
local chain_gen_r2 = function(param, state, state_x, ...)
    if state_x == nil then
        local i = state[1]
        i = i + 1
        if param[3 * i - 1] == nil then
            return nil
        end
        local state_x = param[3 * i]
        return chain_gen_r1(param, {i, state_x})
    end
    return {state[1], state_x}, ...
end

chain_gen_r1 = function(param, state)
    local i, state_x = state[1], state[2]
    local gen_x, param_x = param[3 * i - 2], param[3 * i - 1]
    return chain_gen_r2(param, state, gen_x(param_x, state[2]))
end

local chain = function(...)
    local n = numargs(...)
    if n == 0 then
        return wrap(nil_gen, nil, nil)
    end

    local param = { [3 * n] = 0 }
    local i, gen_x, param_x, state_x
    for i=1,n,1 do
        local elem = select(i, ...)
        gen_x, param_x, state_x = iter(elem)
        param[3 * i - 2] = gen_x
        param[3 * i - 1] = param_x
        param[3 * i] = state_x
    end

    return wrap(chain_gen_r1, param, {1, param[3]})
end
methods.chain = chain
exports.chain = chain

--------------------------------------------------------------------------------
-- Operators
--------------------------------------------------------------------------------

local operator = {
    ----------------------------------------------------------------------------
    -- Comparison operators
    ----------------------------------------------------------------------------
    lt  = function(a, b) return a < b end,
    le  = function(a, b) return a <= b end,
    eq  = function(a, b) return a == b end,
    ne  = function(a, b) return a ~= b end,
    ge  = function(a, b) return a >= b end,
    gt  = function(a, b) return a > b end,

    ----------------------------------------------------------------------------
    -- Arithmetic operators
    ----------------------------------------------------------------------------
    add = function(a, b) return a + b end,
    div = function(a, b) return a / b end,
    floordiv = function(a, b) return math.floor(a/b) end,
    intdiv = function(a, b)
        local q = a / b
        if a >= 0 then return math.floor(q) else return math.ceil(q) end
    end,
    mod = function(a, b) return a % b end,
    mul = function(a, b) return a * b end,
    neq = function(a) return -a end,
    unm = function(a) return -a end, -- an alias
    pow = function(a, b) return a ^ b end,
    sub = function(a, b) return a - b end,
    truediv = function(a, b) return a / b end,

    ----------------------------------------------------------------------------
    -- String operators
    ----------------------------------------------------------------------------
    concat = function(a, b) return a..b end,
    len = function(a) return #a end,
    length = function(a) return #a end, -- an alias

    ----------------------------------------------------------------------------
    -- Logical operators
    ----------------------------------------------------------------------------
    land = function(a, b) return a and b end,
    lor = function(a, b) return a or b end,
    lnot = function(a) return not a end,
    truth = function(a) return not not a end,
}
exports.operator = operator
methods.operator = operator
exports.op = operator
methods.op = operator

--------------------------------------------------------------------------------
-- module definitions
--------------------------------------------------------------------------------

-- a special syntax sugar to export all functions to the global table
setmetatable(exports, {
    __call = function(t, override)
        for k, v in pairs(t) do
            if rawget(_G, k) ~= nil then
                local msg = 'function ' .. k .. ' already exists in global scope.'
                if override then
                    rawset(_G, k, v)
                    print('WARNING: ' .. msg .. ' Overwritten.')
                else
                    print('NOTICE: ' .. msg .. ' Skipped.')
                end
            else
                rawset(_G, k, v)
            end
        end
    end,
})

return exports