summaryrefslogtreecommitdiffhomepage
path: root/chapel.html.markdown
blob: 68ce49cd2672612018f20c10a154597c79f2f16a (plain)
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
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
---
language: chapel
filename: learnchapel.chpl
contributors:
    - ["Ian J. Bertolacci", "http://www.cs.colostate.edu/~ibertola/"]
    - ["Ben Harshbarger", "http://github.com/benharsh/"]
---

You can read all about Chapel at [Cray's official Chapel website](http://chapel.cray.com).
In short, Chapel is an open-source, high-productivity, parallel-programming
language in development at Cray Inc., and is designed to run on multi-core PCs
as well as multi-kilocore supercomputers.

More information and support can be found at the bottom of this document.

```chapel
// Comments are C-family style

// one line comment
/*
 multi-line comment
*/

// Basic printing

write("Hello, ");
writeln("World!");

// write and writeln can take a list of things to print.
// Each thing is printed right next to the others, so include your spacing!
writeln("There are ", 3, " commas (\",\") in this line of code");

// Different output channels:
stdout.writeln("This goes to standard output, just like plain writeln() does");
stderr.writeln("This goes to standard error");


// Variables don't have to be explicitly typed as long as
// the compiler can figure out the type that it will hold.
// 10 is an int, so myVar is implicitly an int
var myVar = 10;
myVar = -10;
var mySecondVar = myVar;
// var anError; would be a compile-time error.

// We can (and should) explicitly type things.
var myThirdVar: real;
var myFourthVar: real = -1.234;
myThirdVar = myFourthVar;

// Types

// There are a number of basic types.
var myInt: int = -1000; // Signed ints
var myUint: uint = 1234; // Unsigned ints
var myReal: real = 9.876; // Floating point numbers
var myImag: imag = 5.0i; // Imaginary numbers
var myCplx: complex = 10 + 9i; // Complex numbers
myCplx = myInt + myImag; // Another way to form complex numbers
var myBool: bool = false; // Booleans
var myStr: string = "Some string..."; // Strings
var singleQuoteStr = 'Another string...'; // String literal with single quotes

// Some types can have sizes.
var my8Int: int(8) = 10; // 8 bit (one byte) sized int;
var my64Real: real(64) = 1.516; // 64 bit (8 bytes) sized real

// Typecasting.
var intFromReal = myReal : int;
var intFromReal2: int = myReal : int;

// Type aliasing.
type chroma = int;        // Type of a single hue
type RGBColor = 3*chroma; // Type representing a full color
var black: RGBColor = (0,0,0);
var white: RGBColor = (255, 255, 255);

// Constants and Parameters

// A const is a constant, and cannot be changed after set in runtime.
const almostPi: real = 22.0/7.0;

// A param is a constant whose value must be known statically at
// compile-time.
param compileTimeConst: int = 16;

// The config modifier allows values to be set at the command line.
// Set with --varCmdLineArg=Value or --varCmdLineArg Value at runtime.
config var varCmdLineArg: int = -123;
config const constCmdLineArg: int = 777;

// config param can be set at compile-time.
// Set with --set paramCmdLineArg=value at compile-time.
config param paramCmdLineArg: bool = false;
writeln(varCmdLineArg, ", ", constCmdLineArg, ", ", paramCmdLineArg);

// References

// ref operates much like a reference in C++. In Chapel, a ref cannot
// be made to alias a variable other than the variable it is initialized with.
// Here, refToActual refers to actual.
var actual = 10;
ref refToActual = actual; 
writeln(actual, " == ", refToActual); // prints the same value
actual = -123; // modify actual (which refToActual refers to)
writeln(actual, " == ", refToActual); // prints the same value
refToActual = 99999999; // modify what refToActual refers to (which is actual)
writeln(actual, " == ", refToActual); // prints the same value

// Operators

// Math operators:
var a: int, thisInt = 1234, thatInt = 5678;
a = thisInt + thatInt;  // Addition
a = thisInt * thatInt;  // Multiplication
a = thisInt - thatInt;  // Subtraction
a = thisInt / thatInt;  // Division
a = thisInt ** thatInt; // Exponentiation
a = thisInt % thatInt;  // Remainder (modulo)

// Logical operators:
var b: bool, thisBool = false, thatBool = true;
b = thisBool && thatBool; // Logical and
b = thisBool || thatBool; // Logical or
b = !thisBool;            // Logical negation

// Relational operators:
b = thisInt > thatInt;           // Greater-than
b = thisInt >= thatInt;          // Greater-than-or-equal-to
b = thisInt < a && a <= thatInt; // Less-than, and, less-than-or-equal-to
b = thisInt != thatInt;          // Not-equal-to
b = thisInt == thatInt;          // Equal-to

// Bitwise operators:
a = thisInt << 10;     // Left-bit-shift by 10 bits;
a = thatInt >> 5;      // Right-bit-shift by 5 bits;
a = ~thisInt;          // Bitwise-negation
a = thisInt ^ thatInt; // Bitwise exclusive-or

// Compound assignment operators:
a += thisInt;          // Addition-equals (a = a + thisInt;)
a *= thatInt;          // Times-equals (a = a * thatInt;)
b &&= thatBool;        // Logical-and-equals (b = b && thatBool;)
a <<= 3;               // Left-bit-shift-equals (a = a << 10;)

// Unlike other C family languages, there are no
// pre/post-increment/decrement operators, such as:
//
// ++j, --j, j++, j--

// Swap operator:
var old_this = thisInt;
var old_that = thatInt;
thisInt <=> thatInt; // Swap the values of thisInt and thatInt
writeln((old_this == thatInt) && (old_that == thisInt));

// Operator overloads can also be defined, as we'll see with procedures.

// Tuples

// Tuples can be of the same type or different types.
var sameTup: 2*int = (10, -1);
var sameTup2 = (11, -6);
var diffTup: (int,real,complex) = (5, 1.928, myCplx);
var diffTupe2 = (7, 5.64, 6.0+1.5i);

// Tuples can be accessed using square brackets or parentheses, and are
// 1-indexed.
writeln("(", sameTup[1], ",", sameTup(2), ")");
writeln(diffTup);

// Tuples can also be written into.
diffTup(1) = -1;

// Tuple values can be expanded into their own variables.
var (tupInt, tupReal, tupCplx) = diffTup;
writeln(diffTup == (tupInt, tupReal, tupCplx));

// They are also useful for writing a list of variables, as is common in debugging.
writeln((a,b,thisInt,thatInt,thisBool,thatBool));

// Control Flow

// if - then - else works just like any other C-family language.
if 10 < 100 then
  writeln("All is well");

if -1 < 1 then
  writeln("Continuing to believe reality");
else
  writeln("Send mathematician, something's wrong");

// You can use parentheses if you prefer.
if (10 > 100) {
  writeln("Universe broken. Please reboot universe.");
}

if a % 2 == 0 {
  writeln(a, " is even.");
} else {
  writeln(a, " is odd.");
}

if a % 3 == 0 {
  writeln(a, " is even divisible by 3.");
} else if a % 3 == 1 {
  writeln(a, " is divided by 3 with a remainder of 1.");
} else {
  writeln(b, " is divided by 3 with a remainder of 2.");
}

// Ternary: if - then - else in a statement.
var maximum = if thisInt < thatInt then thatInt else thisInt;

// select statements are much like switch statements in other languages.
// However, select statements don't cascade like in C or Java.
var inputOption = "anOption";
select inputOption {
  when "anOption" do writeln("Chose 'anOption'");
  when "otherOption" {
    writeln("Chose 'otherOption'");
    writeln("Which has a body");
  }
  otherwise {
    writeln("Any other Input");
    writeln("the otherwise case doesn't need a do if the body is one line");
  }
}

// while and do-while loops also behave like their C counterparts.
var j: int = 1;
var jSum: int = 0;
while (j <= 1000) {
  jSum += j;
  j += 1;
}
writeln(jSum);

do {
  jSum += j;
  j += 1;
} while (j <= 10000);
writeln(jSum);

// for loops are much like those in python in that they iterate over a
// range. Ranges (like the 1..10 expression below) are a first-class object
// in Chapel, and as such can be stored in variables.
for i in 1..10 do write(i, ", ");
writeln();

var iSum: int = 0;
for i in 1..1000 {
  iSum += i;
}
writeln(iSum);

for x in 1..10 {
  for y in 1..10 {
    write((x,y), "\t");
  }
  writeln();
}

// Ranges and Domains

// For-loops and arrays both use ranges and domains to define an index set that
// can be iterated over. Ranges are single dimensional integer indices, while
// domains can be multi-dimensional and represent indices of different types.

// They are first-class citizen types, and can be assigned into variables.
var range1to10: range = 1..10;  // 1, 2, 3, ..., 10
var range2to11 = 2..11; // 2, 3, 4, ..., 11
var rangeThisToThat: range = thisInt..thatInt; // using variables
var rangeEmpty: range = 100..-100; // this is valid but contains no indices

// Ranges can be unbounded.
var range1toInf: range(boundedType=BoundedRangeType.boundedLow) = 1.. ; // 1, 2, 3, 4, 5, ...
var rangeNegInfTo1 = ..1; // ..., -4, -3, -2, -1, 0, 1

// Ranges can be strided (and reversed) using the by operator.
var range2to10by2: range(stridable=true) = 2..10 by 2; // 2, 4, 6, 8, 10
var reverse2to10by2 = 2..10 by -2; // 10, 8, 6, 4, 2

var trapRange = 10..1 by -1; // Do not be fooled, this is still an empty range
writeln("Size of range '", trapRange, "' = ", trapRange.length);

// Note: range(boundedType= ...) and range(stridable= ...) are only
// necessary if we explicitly type the variable.

// The end point of a range can be determined using the count (#) operator.
var rangeCount: range = -5..#12; // range from -5 to 6

// Operators can be mixed.
var rangeCountBy: range(stridable=true) = -5..#12 by 2; // -5, -3, -1, 1, 3, 5
writeln(rangeCountBy);

// Properties of the range can be queried.
// In this example, printing the first index, last index, number of indices,
// stride, and if 2 is include in the range.
writeln((rangeCountBy.first, rangeCountBy.last, rangeCountBy.length,
           rangeCountBy.stride, rangeCountBy.member(2)));

for i in rangeCountBy {
  write(i, if i == rangeCountBy.last then "\n" else ", ");
}

// Rectangular domains are defined using the same range syntax,
// but they are required to be bounded (unlike ranges).
var domain1to10: domain(1) = {1..10};        // 1D domain from 1..10;
var twoDimensions: domain(2) = {-2..2,0..2}; // 2D domain over product of ranges
var thirdDim: range = 1..16;
var threeDims: domain(3) = {thirdDim, 1..10, 5..10}; // using a range variable

// Domains can also be resized
var resizedDom = {1..10};
writeln("before, resizedDom = ", resizedDom);
resizedDom = {-10..#10};
writeln("after, resizedDom = ", resizedDom);

// Indices can be iterated over as tuples.
for idx in twoDimensions do
  write(idx, ", ");
writeln();

// These tuples can also be deconstructed.
for (x,y) in twoDimensions {
  write("(", x, ", ", y, ")", ", ");
}
writeln();

// Associative domains act like sets.
var stringSet: domain(string); // empty set of strings
stringSet += "a";
stringSet += "b";
stringSet += "c";
stringSet += "a"; // Redundant add "a"
stringSet -= "c"; // Remove "c"
writeln(stringSet.sorted());

// Associative domains can also have a literal syntax
var intSet = {1, 2, 4, 5, 100};

// Both ranges and domains can be sliced to produce a range or domain with the
// intersection of indices.
var rangeA = 1.. ; // range from 1 to infinity
var rangeB =  ..5; // range from negative infinity to 5
var rangeC = rangeA[rangeB]; // resulting range is 1..5
writeln((rangeA, rangeB, rangeC));

var domainA = {1..10, 5..20};
var domainB = {-5..5, 1..10};
var domainC = domainA[domainB];
writeln((domainA, domainB, domainC));

// Arrays

// Arrays are similar to those of other languages.
// Their sizes are defined using domains that represent their indices.
var intArray: [1..10] int;
var intArray2: [{1..10}] int; // equivalent

// They can be accessed using either brackets or parentheses
for i in 1..10 do
  intArray[i] = -i;
writeln(intArray);

// We cannot access intArray[0] because it exists outside
// of the index set, {1..10}, we defined it to have.
// intArray[11] is illegal for the same reason.
var realDomain: domain(2) = {1..5,1..7};
var realArray: [realDomain] real;
var realArray2: [1..5,1..7] real;   // equivalent
var realArray3: [{1..5,1..7}] real; // equivalent

for i in 1..5 {
  for j in realDomain.dim(2) {   // Only use the 2nd dimension of the domain
    realArray[i,j] = -1.61803 * i + 0.5 * j;  // Access using index list
    var idx: 2*int = (i,j);                   // Note: 'index' is a keyword
    realArray[idx] = - realArray[(i,j)];      // Index using tuples
  }
}

// Arrays have domains as members, and can be iterated over as normal.
for idx in realArray.domain {  // Again, idx is a 2*int tuple
  realArray[idx] = 1 / realArray[idx[1], idx[2]]; // Access by tuple and list
}

writeln(realArray);

// The values of an array can also be iterated directly.
var rSum: real = 0;
for value in realArray {
  rSum += value; // Read a value
  value = rSum;  // Write a value
}
writeln(rSum, "\n", realArray);

// Associative arrays (dictionaries) can be created using associative domains.
var dictDomain: domain(string) = { "one", "two" };
var dict: [dictDomain] int = ["one" => 1, "two" => 2];
dict["three"] = 3; // Adds 'three' to 'dictDomain' implicitly
for key in dictDomain.sorted() do
  writeln(dict[key]);

// Arrays can be assigned to each other in a few different ways.
// These arrays will be used in the example.
var thisArray : [0..5] int = [0,1,2,3,4,5];
var thatArray : [0..5] int;

// First, simply assign one to the other. This copies thisArray into
// thatArray, instead of just creating a reference. Therefore, modifying
// thisArray does not also modify thatArray.

thatArray = thisArray;
thatArray[1] = -1;
writeln((thisArray, thatArray));

// Assign a slice from one array to a slice (of the same size) in the other.
thatArray[4..5] = thisArray[1..2];
writeln((thisArray, thatArray));

// Operations can also be promoted to work on arrays. 'thisPlusThat' is also
// an array.
var thisPlusThat = thisArray + thatArray;
writeln(thisPlusThat);

// Moving on, arrays and loops can also be expressions, where the loop
// body's expression is the result of each iteration.
var arrayFromLoop = for i in 1..10 do i;
writeln(arrayFromLoop);

// An expression can result in nothing, such as when filtering with an if-expression.
var evensOrFives = for i in 1..10 do if (i % 2 == 0 || i % 5 == 0) then i;

writeln(arrayFromLoop);

// Array expressions can also be written with a bracket notation.
// Note: this syntax uses the forall parallel concept discussed later.
var evensOrFivesAgain = [i in 1..10] if (i % 2 == 0 || i % 5 == 0) then i;

// They can also be written over the values of the array.
arrayFromLoop = [value in arrayFromLoop] value + 1;


// Procedures

// Chapel procedures have similar syntax functions in other languages. 
proc fibonacci(n : int) : int {
  if n <= 1 then return n;
  return fibonacci(n-1) + fibonacci(n-2);
}

// Input parameters can be untyped to create a generic procedure.
proc doublePrint(thing): void {
  write(thing, " ", thing, "\n");
}

// The return type can be inferred, as long as the compiler can figure it out.
proc addThree(n) {
  return n + 3;
}

doublePrint(addThree(fibonacci(20)));

// It is also possible to take a variable number of parameters.
proc maxOf(x ...?k) {
  // x refers to a tuple of one type, with k elements
  var maximum = x[1];
  for i in 2..k do maximum = if maximum < x[i] then x[i] else maximum;
  return maximum;
}
writeln(maxOf(1, -10, 189, -9071982, 5, 17, 20001, 42));

// Procedures can have default parameter values, and
// the parameters can be named in the call, even out of order.
proc defaultsProc(x: int, y: real = 1.2634): (int,real) {
  return (x,y);
}

writeln(defaultsProc(10));
writeln(defaultsProc(x=11));
writeln(defaultsProc(x=12, y=5.432));
writeln(defaultsProc(y=9.876, x=13));

// The ? operator is called the query operator, and is used to take
// undetermined values like tuple or array sizes and generic types.
// For example, taking arrays as parameters. The query operator is used to
// determine the domain of A. This is uesful for defining the return type,
// though it's not required.
proc invertArray(A: [?D] int): [D] int{
  for a in A do a = -a;
  return A;
}

writeln(invertArray(intArray));

// We can query the type of arguments to generic procedures.
// Here we define a procedure that takes two arguments of
// the same type, yet we don't define what that type is.
proc genericProc(arg1 : ?valueType, arg2 : valueType): void {
  select(valueType) {
    when int do writeln(arg1, " and ", arg2, " are ints");
    when real do writeln(arg1, " and ", arg2, " are reals");
    otherwise writeln(arg1, " and ", arg2, " are somethings!");
  }
}

genericProc(1, 2);
genericProc(1.2, 2.3);
genericProc(1.0+2.0i, 3.0+4.0i);

// We can also enforce a form of polymorphism with the where clause
// This allows the compiler to decide which function to use.
// Note: That means that all information needs to be known at compile-time.
// The param modifier on the arg is used to enforce this constraint.
proc whereProc(param N : int): void
 where (N > 0) {
  writeln("N is greater than 0");
}

proc whereProc(param N : int): void
 where (N < 0) {
  writeln("N is less than 0");
}

whereProc(10);
whereProc(-1);

// whereProc(0) would result in a compiler error because there
// are no functions that satisfy the where clause's condition.
// We could have defined a whereProc without a where clause
// that would then have served as a catch all for all the other cases
// (of which there is only one).

// where clauses can also be used to constrain based on argument type.
proc whereType(x: ?t) where t == int {
  writeln("Inside 'int' version of 'whereType': ", x);
}

proc whereType(x: ?t) {
  writeln("Inside general version of 'whereType': ", x);
}

whereType(42);
whereType("hello");

// Intents

/* Intent modifiers on the arguments convey how those arguments are passed to the procedure.

     * in: copy arg in, but not out
     * out: copy arg out, but not in
     * inout: copy arg in, copy arg out
     * ref: pass arg by reference
*/
proc intentsProc(in inarg, out outarg, inout inoutarg, ref refarg) {
  writeln("Inside Before: ", (inarg, outarg, inoutarg, refarg));
  inarg = inarg + 100;
  outarg = outarg + 100;
  inoutarg = inoutarg + 100;
  refarg = refarg + 100;
  writeln("Inside After: ", (inarg, outarg, inoutarg, refarg));
}

var inVar: int = 1;
var outVar: int = 2;
var inoutVar: int = 3;
var refVar: int = 4;
writeln("Outside Before: ", (inVar, outVar, inoutVar, refVar));
intentsProc(inVar, outVar, inoutVar, refVar);
writeln("Outside After: ", (inVar, outVar, inoutVar, refVar));

// Similarly, we can define intents on the return type.
// refElement returns a reference to an element of array.
// This makes more practical sense for class methods where references to
// elements in a data-structure are returned via a method or iterator.
proc refElement(array : [?D] ?T, idx) ref : T {
  return array[idx];
}

var myChangingArray : [1..5] int = [1,2,3,4,5];
writeln(myChangingArray);
ref refToElem = refElement(myChangingArray, 5); // store reference to element in ref variable
writeln(refToElem);
refToElem = -2; // modify reference which modifies actual value in array
writeln(refToElem);
writeln(myChangingArray);

// Operator Definitions

// Chapel allows for operators to be overloaded.
// We can define the unary operators:
// + - ! ~
// and the binary operators:
// + - * / % ** == <= >= < > << >> & | ˆ by
// += -= *= /= %= **= &= |= ˆ= <<= >>= <=>

// Boolean exclusive or operator.
proc ^(left : bool, right : bool): bool {
  return (left || right) && !(left && right);
}

writeln(true  ^ true);
writeln(false ^ true);
writeln(true  ^ false);
writeln(false ^ false);

// Define a * operator on any two types that returns a tuple of those types.
proc *(left : ?ltype, right : ?rtype): (ltype, rtype) {
  writeln("\tIn our '*' overload!");
  return (left, right);
}

writeln(1 * "a"); // Uses our * operator.
writeln(1 * 2);   // Uses the default * operator.

//  Note: You could break everything if you get careless with your overloads.
//  This here will break everything. Don't do it.

/*
    proc +(left: int, right: int): int {
      return left - right;
    }
*/

// Iterators

// Iterators are sisters to the procedure, and almost everything about
// procedures also applies to iterators. However, instead of returning a single
// value, iterators may yield multiple values to a loop.
//
// This is useful when a complicated set or order of iterations is needed, as
// it allows the code defining the iterations to be separate from the loop
// body.
iter oddsThenEvens(N: int): int {
  for i in 1..N by 2 do
    yield i; // yield values instead of returning.
  for i in 2..N by 2 do
    yield i;
}

for i in oddsThenEvens(10) do write(i, ", ");
writeln();

// Iterators can also yield conditionally, the result of which can be nothing
iter absolutelyNothing(N): int {
  for i in 1..N {
    if N < i { // Always false
      yield i;     // Yield statement never happens
    }
  }
}

for i in absolutelyNothing(10) {
  writeln("Woa there! absolutelyNothing yielded ", i);
}

// We can zipper together two or more iterators (who have the same number
// of iterations) using zip() to create a single zipped iterator, where each
// iteration of the zipped iterator yields a tuple of one value yielded
// from each iterator.
for (positive, negative) in zip(1..5, -5..-1) do
  writeln((positive, negative));

// Zipper iteration is quite important in the assignment of arrays,
// slices of arrays, and array/loop expressions.
var fromThatArray : [1..#5] int = [1,2,3,4,5];
var toThisArray : [100..#5] int;

// Some zipper operations implement other operations.
// The first statement and the loop are equivalent.
toThisArray = fromThatArray;
for (i,j) in zip(toThisArray.domain, fromThatArray.domain) {
  toThisArray[i] = fromThatArray[j];
}

// These two chunks are also equivalent.
toThisArray = [j in -100..#5] j;
writeln(toThisArray);

for (i, j) in zip(toThisArray.domain, -100..#5) {
  toThisArray[i] = j;
}
writeln(toThisArray);

// This is very important in understanding why this statement exhibits a
// runtime error.

/*
  var iterArray : [1..10] int = [i in 1..10] if (i % 2 == 1) then i;
*/

// Even though the domain of the array and the loop-expression are
// the same size, the body of the expression can be thought of as an iterator.
// Because iterators can yield nothing, that iterator yields a different number
// of things than the domain of the array or loop, which is not allowed.

// Classes

// Classes are similar to those in C++ and Java, allocated on the heap.
class MyClass {

// Member variables
  var memberInt : int;
  var memberBool : bool = true;

// Explicitly defined initializer.
// We also get the compiler-generated initializer, with one argument per field.
// Note that soon there will be no compiler-generated initializer when we
// define any initializer(s) explicitly.
  proc MyClass(val : real) {
    this.memberInt = ceil(val): int;
  }

// Explicitly defined deinitializer.
// If we did not write one, we would get the compiler-generated deinitializer,
// which has an empty body.
  proc deinit() {
    writeln("MyClass deinitializer called ", (this.memberInt, this.memberBool));
  }

// Class methods.
  proc setMemberInt(val: int) {
    this.memberInt = val;
  }

  proc setMemberBool(val: bool) {
    this.memberBool = val;
  }

  proc getMemberInt(): int{
    return this.memberInt;
  }

  proc getMemberBool(): bool {
    return this.memberBool;
  }
} // end MyClass

// Call compiler-generated initializer, using default value for memberBool.
var myObject = new MyClass(10);
    myObject = new MyClass(memberInt = 10); // Equivalent
writeln(myObject.getMemberInt());

// Same, but provide a memberBool value explicitly.
var myDiffObject = new MyClass(-1, true);
    myDiffObject = new MyClass(memberInt = -1,
                                memberBool = true); // Equivalent
writeln(myDiffObject);

// Call the initializer we wrote.
var myOtherObject = new MyClass(1.95);
    myOtherObject = new MyClass(val = 1.95); // Equivalent
writeln(myOtherObject.getMemberInt());

// We can define an operator on our class as well, but
// the definition has to be outside the class definition.
proc +(A : MyClass, B : MyClass) : MyClass {
  return new MyClass(memberInt = A.getMemberInt() + B.getMemberInt(),
                      memberBool = A.getMemberBool() || B.getMemberBool());
}

var plusObject = myObject + myDiffObject;
writeln(plusObject);

// Destruction.
delete myObject;
delete myDiffObject;
delete myOtherObject;
delete plusObject;

// Classes can inherit from one or more parent classes
class MyChildClass : MyClass {
  var memberComplex: complex;
}

// Here's an example of generic classes.
class GenericClass {
  type classType;
  var classDomain: domain(1);
  var classArray: [classDomain] classType;

// Explicit constructor.
  proc GenericClass(type classType, elements : int) {
    this.classDomain = {1..#elements};
  }

// Copy constructor.
// Note: We still have to put the type as an argument, but we can
// default to the type of the other object using the query (?) operator.
// Further, we can take advantage of this to allow our copy constructor
// to copy classes of different types and cast on the fly.
  proc GenericClass(other : GenericClass(?otherType),
                     type classType = otherType) {
    this.classDomain = other.classDomain;
    // Copy and cast
    for idx in this.classDomain do this[idx] = other[idx] : classType;
  }

// Define bracket notation on a GenericClass
// object so it can behave like a normal array
// i.e. objVar[i] or objVar(i)
  proc this(i : int) ref : classType {
    return this.classArray[i];
  }

// Define an implicit iterator for the class
// to yield values from the array to a loop
// i.e. for i in objVar do ...
  iter these() ref : classType {
    for i in this.classDomain do
      yield this[i];
  }
} // end GenericClass

// We can assign to the member array of the object using the bracket
// notation that we defined.
var realList = new GenericClass(real, 10);
for i in realList.classDomain do realList[i] = i + 1.0;

// We can iterate over the values in our list with the iterator
// we defined.
for value in realList do write(value, ", ");
writeln();

// Make a copy of realList using the copy constructor.
var copyList = new GenericClass(realList);
for value in copyList do write(value, ", ");
writeln();

// Make a copy of realList and change the type, also using the copy constructor.
var copyNewTypeList = new GenericClass(realList, int);
for value in copyNewTypeList do write(value, ", ");
writeln();


// Modules

// Modules are Chapel's way of managing name spaces.
// The files containing these modules do not need to be named after the modules
// (as in Java), but files implicitly name modules.
// For example, this file implicitly names the learnChapelInYMinutes module

module OurModule {

// We can use modules inside of other modules.
// Time is one of the standard modules.
  use Time;

// We'll use this procedure in the parallelism section.
  proc countdown(seconds: int) {
    for i in 1..seconds by -1 {
      writeln(i);
      sleep(1);
    }
  }

// It is possible to create arbitrarily deep module nests.
// i.e. submodules of OurModule
  module ChildModule {
    proc foo() {
      writeln("ChildModule.foo()");
    }
  }

  module SiblingModule {
    proc foo() {
      writeln("SiblingModule.foo()");
    }
  }
} // end OurModule

// Using OurModule also uses all the modules it uses.
// Since OurModule uses Time, we also use Time.
use OurModule;

// At this point we have not used ChildModule or SiblingModule so
// their symbols (i.e. foo) are not available to us. However, the module
// names are available, and we can explicitly call foo() through them.
SiblingModule.foo();
OurModule.ChildModule.foo();

// Now we use ChildModule, enabling unqualified calls.
use ChildModule;
foo();

// Parallelism

// In other languages, parallelism is typically done with
// complicated libraries and strange class structure hierarchies.
// Chapel has it baked right into the language.

// We can declare a main procedure, but all the code above main still gets
// executed.
proc main() {
  writeln("PARALLELISM START");

// A begin statement will spin the body of that statement off
// into one new task.
// A sync statement will ensure that the progress of the main
// task will not progress until the children have synced back up.

  sync {
    begin { // Start of new task's body
      var a = 0;
      for i in 1..1000 do a += 1;
      writeln("Done: ", a);
    } // End of new tasks body
    writeln("spun off a task!");
  }
  writeln("Back together");

  proc printFibb(n: int) {
    writeln("fibonacci(",n,") = ", fibonacci(n));
  }

// A cobegin statement will spin each statement of the body into one new
// task. Notice here that the prints from each statement may happen in any
// order.
  cobegin {
    printFibb(20); // new task
    printFibb(10); // new task
    printFibb(5);  // new task
    {
      // This is a nested statement body and thus is a single statement
      // to the parent statement, executed by a single task.
      writeln("this gets");
      writeln("executed as");
      writeln("a whole");
    }
  }

// A coforall loop will create a new task for EACH iteration.
// Again we see that prints happen in any order.
// NOTE: coforall should be used only for creating tasks!
// Using it to iterating over a structure is very a bad idea!
  var num_tasks = 10; // Number of tasks we want
  coforall taskID in 1..#num_tasks {
    writeln("Hello from task# ", taskID);
  }

// forall loops are another parallel loop, but only create a smaller number
// of tasks, specifically --dataParTasksPerLocale= number of tasks.
  forall i in 1..100 {
    write(i, ", ");
  }
  writeln();

// Here we see that there are sections that are in order, followed by
// a section that would not follow (e.g. 1, 2, 3, 7, 8, 9, 4, 5, 6,).
// This is because each task is taking on a chunk of the range 1..10
// (1..3, 4..6, or 7..9) doing that chunk serially, but each task happens
// in parallel. Your results may depend on your machine and configuration

// For both the forall and coforall loops, the execution of the
// parent task will not continue until all the children sync up.

// forall loops are particularly useful for parallel iteration over arrays.
// Lets run an experiment to see how much faster a parallel loop is
  use Time; // Import the Time module to use Timer objects
  var timer: Timer;
  var myBigArray: [{1..4000,1..4000}] real; // Large array we will write into

// Serial Experiment:
  timer.start(); // Start timer
  for (x,y) in myBigArray.domain { // Serial iteration
    myBigArray[x,y] = (x:real) / (y:real);
  }
  timer.stop(); // Stop timer
  writeln("Serial: ", timer.elapsed()); // Print elapsed time
  timer.clear(); // Clear timer for parallel loop

// Parallel Experiment:
  timer.start(); // start timer
  forall (x,y) in myBigArray.domain { // Parallel iteration
    myBigArray[x,y] = (x:real) / (y:real);
  }
  timer.stop(); // Stop timer
  writeln("Parallel: ", timer.elapsed()); // Print elapsed time
  timer.clear();

// You may have noticed that (depending on how many cores you have)
// the parallel loop went faster than the serial loop.

// The bracket style loop-expression described
// much earlier implicitly uses a forall loop.
  [val in myBigArray] val = 1 / val; // Parallel operation

// Atomic variables, common to many languages, are ones whose operations
// occur uninterrupted. Multiple threads can therefore modify atomic
// variables and can know that their values are safe.
// Chapel atomic variables can be of type bool, int,
// uint, and real.
  var uranium: atomic int;
  uranium.write(238);      // atomically write a variable
  writeln(uranium.read()); // atomically read a variable

// Atomic operations are described as functions, so you can define your own.
  uranium.sub(3); // atomically subtract a variable
  writeln(uranium.read());

  var replaceWith = 239;
  var was = uranium.exchange(replaceWith);
  writeln("uranium was ", was, " but is now ", replaceWith);

  var isEqualTo = 235;
  if uranium.compareExchange(isEqualTo, replaceWith) {
    writeln("uranium was equal to ", isEqualTo,
             " so replaced value with ", replaceWith);
  } else {
    writeln("uranium was not equal to ", isEqualTo,
             " so value stays the same...  whatever it was");
  }

  sync {
    begin { // Reader task
      writeln("Reader: waiting for uranium to be ", isEqualTo);
      uranium.waitFor(isEqualTo);
      writeln("Reader: uranium was set (by someone) to ", isEqualTo);
    }

    begin { // Writer task
      writeln("Writer: will set uranium to the value ", isEqualTo, " in...");
      countdown(3);
      uranium.write(isEqualTo);
    }
  }

// sync variables have two states: empty and full.
// If you read an empty variable or write a full variable, you are waited
// until the variable is full or empty again.
  var someSyncVar$: sync int; // varName$ is a convention not a law.
  sync {
    begin { // Reader task
      writeln("Reader: waiting to read.");
      var read_sync = someSyncVar$;
      writeln("Reader: value is ", read_sync);
    }

    begin { // Writer task
      writeln("Writer: will write in...");
      countdown(3);
      someSyncVar$ = 123;
    }
  }

// single vars can only be written once. A read on an unwritten single
// results in a wait, but when the variable has a value it can be read
// indefinitely.
  var someSingleVar$: single int; // varName$ is a convention not a law.
  sync {
    begin { // Reader task
      writeln("Reader: waiting to read.");
      for i in 1..5 {
        var read_single = someSingleVar$;
        writeln("Reader: iteration ", i,", and the value is ", read_single);
      }
    }

    begin { // Writer task
      writeln("Writer: will write in...");
      countdown(3);
      someSingleVar$ = 5; // first and only write ever.
    }
  }

// Heres an example using atomics and a sync variable to create a
// count-down mutex (also known as a multiplexer).
  var count: atomic int; // our counter
  var lock$: sync bool;   // the mutex lock

  count.write(2);       // Only let two tasks in at a time.
  lock$.writeXF(true);  // Set lock$ to full (unlocked)
  // Note: The value doesnt actually matter, just the state
  // (full:unlocked / empty:locked)
  // Also, writeXF() fills (F) the sync var regardless of its state (X)

  coforall task in 1..#5 { // Generate tasks
    // Create a barrier
    do {
      lock$;                 // Read lock$ (wait)
    } while (count.read() < 1); // Keep waiting until a spot opens up

    count.sub(1);          // decrement the counter
    lock$.writeXF(true); // Set lock$ to full (signal)

    // Actual 'work'
    writeln("Task #", task, " doing work.");
    sleep(2);

    count.add(1);        // Increment the counter
    lock$.writeXF(true); // Set lock$ to full (signal)
  }

// We can define the operations + * & | ^ && || min max minloc maxloc
// over an entire array using scans and reductions.
// Reductions apply the operation over the entire array and
// result in a scalar value.
  var listOfValues: [1..10] int = [15,57,354,36,45,15,456,8,678,2];
  var sumOfValues = + reduce listOfValues;
  var maxValue = max reduce listOfValues; // 'max' give just max value

// maxloc gives max value and index of the max value.
// Note: We have to zip the array and domain together with the zip iterator.
  var (theMaxValue, idxOfMax) = maxloc reduce zip(listOfValues,
                                                  listOfValues.domain);

  writeln((sumOfValues, maxValue, idxOfMax, listOfValues[idxOfMax]));

// Scans apply the operation incrementally and return an array with the
// values of the operation at that index as it progressed through the
// array from array.domain.low to array.domain.high.
  var runningSumOfValues = + scan listOfValues;
  var maxScan = max scan listOfValues;
  writeln(runningSumOfValues);
  writeln(maxScan);
} // end main()
```

Who is this tutorial for?
-------------------------

This tutorial is for people who want to learn the ropes of chapel without
having to hear about what fiber mixture the ropes are, or how they were
braided, or how the braid configurations differ between one another. It won't
teach you how to develop amazingly performant code, and it's not exhaustive.
Refer to the [language specification](http://chapel.cray.com/language.html) and
the [module documentation](http://chapel.cray.com/docs/latest/) for more
details.

Occasionally check back here and on the [Chapel site](http://chapel.cray.com)
to see if more topics have been added or more tutorials created.

### What this tutorial is lacking:

 * Exposition of the [standard modules](http://chapel.cray.com/docs/latest/modules/modules.html)
 * Multiple Locales (distributed memory system)
 * Records
 * Parallel iterators

Your input, questions, and discoveries are important to the developers!
-----------------------------------------------------------------------

The Chapel language is still in-development (version 1.15.0), so there are
occasional hiccups with performance and language features. The more information
you give the Chapel development team about issues you encounter or features you
would like to see, the better the language becomes. Feel free to email the team
and other developers through the [sourceforge email lists](https://sourceforge.net/p/chapel/mailman).

If you're really interested in the development of the compiler or contributing
to the project, [check out the master GitHub repository](https://github.com/chapel-lang/chapel).
It is under the [Apache 2.0 License](http://www.apache.org/licenses/LICENSE-2.0).

Installing the Compiler
-----------------------

Chapel can be built and installed on your average 'nix machine (and cygwin).
[Download the latest release version](https://github.com/chapel-lang/chapel/releases/)
and it's as easy as

 1. `tar -xvf chapel-1.15.0.tar.gz`
 2. `cd chapel-1.15.0`
 3. `source util/setchplenv.bash # or .sh or .csh or .fish`
 4. `make`
 5. `make check # optional`

You will need to `source util/setchplenv.EXT` from within the Chapel directory
(`$CHPL_HOME`) every time your terminal starts so it's suggested that you drop
that command in a script that will get executed on startup (like .bashrc).

Chapel is easily installed with Brew for OS X

 1. `brew update`
 2. `brew install chapel`

Compiling Code
--------------

Builds like other compilers:

`chpl myFile.chpl -o myExe`

Notable arguments:

 * `--fast`: enables a number of optimizations and disables array bounds
   checks. Should only enable when application is stable.
 * `--set <Symbol Name>=<Value>`: set config param `<Symbol Name>` to `<Value>`
   at compile-time.
 * `--main-module <Module Name>`: use the main() procedure found in the module
   `<Module Name>` as the executable's main.
 * `--module-dir <Directory>`: includes `<Directory>` in the module search path.