aboutsummaryrefslogtreecommitdiff
path: root/lab2/variables-values-lab.ipynb
blob: 0a7619a5018350293d012b8f57caf6d97c9562fc (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
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "e5c7e407-80c5-4211-9055-d94737de0b8d",
   "metadata": {},
   "source": [
    "$\\newcommand{\\TirName}[1]{\\text{\\small #1}}\n",
    "\\newcommand{\\inferrule}[3][]{\n",
    "  \\let\\and\\qquad\n",
    "  \\begin{array}{@{}l@{}}\n",
    "  \\TirName{#1}\n",
    "  \\\\\n",
    "  \\displaystyle\n",
    "  \\frac{#2}{#3}\n",
    "  \\end{array}\n",
    "}\n",
    "\\newcommand{\\infer}[3][]{\\inferrule[#1]{#2}{#3}}\n",
    "$\n",
    "\n",
    "# Lab: Basic Values, Variables, and Judgments\n",
    "\n",
    "<!-- 3 Expressions -->\n",
    "\n",
    "<!-- 4 Binding and Scope -->\n",
    "\n",
    "<!-- 8 Recursion -->\n",
    "\n",
    "<!-- 9 Inductive Data Types -->\n",
    "\n",
    "<!-- 11 Concrete Syntax -->\n",
    "\n",
    "<!-- 12 Abstract Syntax and Parsing -->\n",
    "\n",
    "<!-- 13 Exercise: Syntax -->\n",
    "\n",
    "<!-- 14 Static Scoping -->\n",
    "\n",
    "<!-- 15 Judgments -->\n",
    "\n",
    "<!-- 16 Variables, Basic Values, and Judgments Lab -->\n",
    "\n",
    "### Learning Goals\n",
    "\n",
    "The primary learning goals of this assignment are to build intuition for\n",
    "the following:\n",
    "\n",
    "-   the distinction between concrete and abstract syntax;\n",
    "-   the relationship between judgment forms/inference rules/judgments\n",
    "    and implementation code;\n",
    "-   using a reference implementation as a definition of semantics;\n",
    "-   variable binding and variable environments.\n",
    "\n",
    "Functional Programming Skills  \n",
    "Recursion over abstract syntax. Representation invariants.\n",
    "\n",
    "Programming Language Ideas  \n",
    "Inductive definitions (grammars/productions/sentences and judgment\n",
    "forms/inference rules/judgments). Semantics (via detective work).\n",
    "\n",
    "### Instructions\n",
    "\n",
    "A version of project files for this lab resides in the public\n",
    "[pppl-lab2](https://github.com/csci3155/pppl-lab2) repository. Please\n",
    "follow separate instructions to get a private clone of this repository\n",
    "for your work.\n",
    "\n",
    "You will be replacing `???` or `case _ => ???` in the `Lab2.scala` file\n",
    "with solutions to the coding exercises described below.\n",
    "\n",
    "**Your lab will not be graded if it does not compile**. You may check\n",
    "compilation with your IDE, `sbt compile`, or with the “sbt compile”\n",
    "GitHub Action provided for you. Comment out any code that does not\n",
    "compile or causes a failing assert. Put in `???` as needed to get\n",
    "something that compiles without error.\n",
    "\n",
    "You may add additional tests to the `Lab2Spec.scala` file. In the\n",
    "`Lab2Spec.scala`, there is empty test class `Lab2StudentSpec` that you\n",
    "can use to separate your tests from the given tests in the `Lab2Spec`\n",
    "class. You are also likely to edit `Lab2.worksheet.sc` for any scratch\n",
    "work. You can also use `Lab2.worksheet.js` to write and experiment in a\n",
    "JavaScript file that you can then parse into a JavaScripty AST (see\n",
    "`Lab2.worksheet.sc`).\n",
    "\n",
    "If you like, you may use this notebook for experimentation. However,\n",
    "**please make sure your code is in `Lab2.scala`; this notebook will not\n",
    "graded.**\n",
    "\n",
    "Recall that you need to switch kernels between running JavaScript and\n",
    "Scala cells.\n",
    "\n",
    "## Interpreter: JavaScripty Calculator\n",
    "\n",
    "In this lab, we extend JavaScripty with additional value types and\n",
    "variable binding. That is, the culmination of the lab is to implement an\n",
    "interpreter for the subset of JavaScript with numbers, booleans,\n",
    "strings, the undefined value, and variable binding."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "id": "fc23196d",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">trait</span> <span class=\"ansi-cyan-fg\">Expr</span>\n",
       "defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">N</span>\n",
       "defined <span class=\"ansi-green-fg\">type</span> <span class=\"ansi-cyan-fg\">Env</span>\n",
       "<span class=\"ansi-cyan-fg\">empty</span>: <span class=\"ansi-green-fg\">Env</span> = <span class=\"ansi-yellow-fg\">Map</span>()</pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "trait Expr                           // e ::=\n",
    "case class N(n: Double) extends Expr //       n\n",
    "\n",
    "type Env = Map[String, Expr]\n",
    "val empty: Env = Map.empty"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "id": "3615c99b",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">eval</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def eval(env: Env, e: Expr): Expr = ???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a2f3b886-b8d3-482d-aac1-088e998593d0",
   "metadata": {},
   "source": [
    "We leave the `Expr` inductive data type mostly undefined for the moment\n",
    "to focus on the type of `eval`.\n",
    "\n",
    "First, observe that the return type of `eval` is an `Expr` (versus\n",
    "`Double` in the previous lab), as we now have more value types. However,\n",
    "`eval` should return an `Expr` that is a JavaScripty value (i.e., is an\n",
    "$e$ `: Expr` such that `isValue(` $e$ `)` returns `true`). The need for\n",
    "the object-language versus meta-language distinction is even more\n",
    "salient here than in the previous lab. For example, it is critical to\n",
    "keep straight that `N(1.0)` is the Scala value representing the\n",
    "JavaScripty value `1.0`.\n",
    "\n",
    "Second, observe that the `eval` function takes a JavaScripty value\n",
    "environment `env: Env` to give meaning to free JavaScripty variables in\n",
    "`e`.\n",
    "\n",
    "These ideas take unpacking, so let us start from the arithmetic\n",
    "sub-language of JavaScripty:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "id": "9088c943",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">Unary</span>\n",
       "defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">Binary</span>\n",
       "defined <span class=\"ansi-green-fg\">trait</span> <span class=\"ansi-cyan-fg\">Uop</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Neg</span>\n",
       "defined <span class=\"ansi-green-fg\">trait</span> <span class=\"ansi-cyan-fg\">Bop</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Plus</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Minus</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Times</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Div</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case class Unary(uop: Uop, e1: Expr) extends Expr            // e ::= uop e1\n",
    "case class Binary(bop: Bop, e1: Expr, e2: Expr) extends Expr //     | e1 bop e2\n",
    "\n",
    "trait Uop                     // uop ::=\n",
    "case object Neg extends Uop   //   -\n",
    "\n",
    "trait Bop                     // bop ::=\n",
    "case object Plus extends Bop  //   +\n",
    "case object Minus extends Bop // | -\n",
    "case object Times extends Bop // | *\n",
    "case object Div extends Bop   // | /"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "44fff901-f124-48fc-bd1d-906b79120db5",
   "metadata": {},
   "source": [
    "Thus far, we have considered only one type of value in our JavaScripty\n",
    "object language: numbers $n$ (which we have considered double-precision\n",
    "floating-point numbers). Specifically, we have stated the following:\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{expressions} & e& \\mathrel{::=}& v\n",
    "\\\\\n",
    "\\text{values} & v& \\mathrel{::=}& n\n",
    "\\end{array}\n",
    "$$\n",
    "\n",
    "Recall from our preliminary discussion about evaluation\n",
    "(**?@sec-evaluation-preliminaries**) that the computational model is a\n",
    "rewriting or reduction of expressions until reaching values. A value is\n",
    "simply an expression that cannot be reduced any further. Thus, we can\n",
    "also consider a unary judgment form $e\\;\\mathsf{value}$ that judges when\n",
    "an expression is a value. $$\n",
    "\\infer[NumVal]{\n",
    "}{\n",
    "  n\\;\\mathsf{value}\n",
    "}\n",
    "$$\n",
    "\n",
    "This judgment form corresponds to the `isValue` function:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "id": "bbf7152f",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">isValue</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def isValue(e: Expr): Boolean = e match {\n",
    "  case N(_) => true\n",
    "  case _ => false\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "8dade6b2-d9fb-47a9-91fd-0e2b6aff8f0a",
   "metadata": {},
   "source": [
    "From our discussion on grammars and inference rules\n",
    "(**?@sec-grammars-and-inference-rules**), we can see this unary judgment\n",
    "form $e\\;\\mathsf{value}$ as defining a syntactic category values $v$.\n",
    "Thus, we freely write grammar productions for $v$ to define the judgment\n",
    "form $e\\;\\mathsf{value}$.\n",
    "\n",
    "<span class=\"theorem-title\">**Exercise 1**</span> For this part of the\n",
    "lab, implement `eval` for the calculator language above (which is the\n",
    "same language as in the previous lab) but now with type\n",
    "`(Env, Expr) => Expr`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "id": "4c173e3a",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">eval</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def eval(env: Env, e: Expr): Expr = ???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "aa64c2db-875f-4d68-a8e9-61eb3951c890",
   "metadata": {},
   "source": [
    "You will not use the `env` parameter yet. You will want to check that\n",
    "your implementation returns JavaScripty values. For example,"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "id": "f88d8980",
   "metadata": {},
   "outputs": [],
   "source": [
    "val e_oneplustwo = Binary(Plus, N(1), N(2))\n",
    "assert( isValue( eval(empty, e_oneplustwo) ) )"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9bffa2f5-4fec-43f1-a871-322dd100c795",
   "metadata": {},
   "source": [
    "## Coercions: Basic Values\n",
    "\n",
    "### Booleans, Strings, and Undefined\n",
    "\n",
    "Like most other languages, JavaScript has other basic value types. Let\n",
    "us extend JavaScripty with Booleans, strings, and the\n",
    "$\\mathbf{undefined}$ value:\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{values} & v& \\mathrel{::=}&\n",
    "b\n",
    "  \\mid\\mathit{str}\n",
    "  \\mid\\mathbf{undefined}\n",
    "\\\\\n",
    "\\text{booleans} & b\n",
    "\\\\\n",
    "\\text{strings} & \\mathit{str}\n",
    "\\end{array}\n",
    "$$\n",
    "\n",
    "Boolean values $b$ are the literals $\\mathbf{true}$ and\n",
    "$\\mathbf{false}$. String values $\\mathit{str}$ are string literals like\n",
    "`\"hi\"` that we do not explicitly define here.\n",
    "\n",
    "The $\\mathbf{undefined}$ literal is a distinguished value that is\n",
    "different than all other values. It is like the unit literal `()` in\n",
    "Scala."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "67096a6c",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">B</span>\n",
       "defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">S</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Undefined</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case class B(b: Boolean) extends Expr  // e ::= b\n",
    "case class S(str: String) extends Expr //     | str\n",
    "case object Undefined extends Expr     //     | undefined"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e9e4fe7c-4dd9-4b7f-85ab-fcbe72cb0292",
   "metadata": {},
   "source": [
    "> **Examples**\n",
    ">\n",
    "> ``` js\n",
    "> true\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> false\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> \"Hello\"\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> \"Hola\"\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> undefined\n",
    "> ```\n",
    "\n",
    "We update our `isValue` function appropriately:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "id": "11b7ec3b",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">isValue</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def isValue(e: Expr): Boolean = e match {\n",
    "  case N(_) | B(_) | S(_) | Undefined => true\n",
    "  case _ => false\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2e5c680f-3806-4f25-a0e0-c568a6935a69",
   "metadata": {},
   "source": [
    "A good exercise here is to reflect on what this code translates to in\n",
    "terms of additional inference rules for the $e\\;\\mathsf{value}$ judgment\n",
    "form.\n",
    "\n",
    "### Expressions\n",
    "\n",
    "Each value type comes with some operations. Our abstract syntax tree has\n",
    "two constructors for unary and binary expressions that are parametrized\n",
    "by unary $\\mathit{uop}$ and binary $\\mathit{bop}$ operators,\n",
    "respectively:\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{expressions} & e& \\mathrel{::=}&\n",
    "  \\mid\\mathop{\\mathit{uop}} e_1\n",
    "  \\mid e_1 \\mathrel{\\mathit{bop}} e_2\n",
    "\\end{array}\n",
    "$$\n",
    "\n",
    "#### Numbers\n",
    "\n",
    "For example, numbers has\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{unary operators} & \\mathit{uop}& \\mathrel{::=}& \\texttt{-}\n",
    "\\\\\n",
    "\\text{binary operators} & \\mathit{bop}& \\mathrel{::=}& \\texttt{+}\\mid\\texttt{-}\\mid\\texttt{*}\\mid\\texttt{/}\n",
    "\\end{array}\n",
    "$$\n",
    "\n",
    "that we considered previously.\n",
    "\n",
    "#### Booleans\n",
    "\n",
    "For booleans, we add unary negation $\\texttt{!}$ and binary conjunction\n",
    "$\\texttt{\\&\\&}$ and disjunction $\\texttt{||}$. $$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{unary operators} & \\mathit{uop}& \\mathrel{::=}&\n",
    "\\texttt{!}\n",
    "\\\\\n",
    "\\text{binary operators} & \\mathit{bop}& \\mathrel{::=}&\n",
    "\\texttt{\\&\\&}\n",
    "\\mid\\texttt{||}\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "88028ed8",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Not</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">And</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Or</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case object Not extends Uop // uop ::= !\n",
    "case object And extends Bop // bop ::= &&\n",
    "case object Or extends Bop  //       | ||"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f21da0e4-59c4-4f78-bd80-ac09e77fa224",
   "metadata": {},
   "source": [
    "> **Examples**\n",
    ">\n",
    "> ``` js\n",
    "> !true\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> true && false\n",
    "> ```\n",
    ">\n",
    "> ``` js\n",
    "> true || false\n",
    "> ```\n",
    "\n",
    "We also expect to be able to elimate booleans with a conditional\n",
    "if-then-else expression: $$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{expressions} & e& \\mathrel{::=}& e_1\\;\\texttt{?}\\;e_2\\;\\texttt{:}\\;e_3\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "05ea3d8a",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">If</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case class If(e1: Expr, e2: Expr, e3: Expr) extends Expr // e ::= e1 ? e2 : e3"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6fe0176b-eb8a-4882-bd33-aa6e6065df6d",
   "metadata": {},
   "source": [
    "We also expect to be able to compare values for equality and disquality\n",
    "and numbers for inequality: $$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{binary operators} & \\mathit{bop}& \\mathrel{::=}&\n",
    "\\texttt{===}\n",
    "\\mid\\texttt{!==}\n",
    "\\mid\\texttt{<}\n",
    "\\mid\\texttt{<=}\n",
    "\\mid\\texttt{>}\n",
    "\\mid\\texttt{>=}\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "47b3dc58",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Eq</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Ne</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Lt</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Le</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Gt</span>\n",
       "defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Ge</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case object Eq extends Bop // bop ::= ===\n",
    "case object Ne extends Bop //       | !==\n",
    "case object Lt extends Bop //       | <\n",
    "case object Le extends Bop //       | <=\n",
    "case object Gt extends Bop //       | >\n",
    "case object Ge extends Bop //       | >="
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ebd33875-524f-4966-96f9-2c1614fef714",
   "metadata": {},
   "source": [
    "#### Strings\n",
    "\n",
    "The one string operation we support in JavaScripty is string\n",
    "concatenation. In JavaScript, string concatenation is written with the\n",
    "binary operator `+`, so we do not need to extend the syntax.\n",
    "\n",
    "> **Examples**\n",
    ">\n",
    "> ``` js\n",
    "> \"Hello\" + \", \" + \"World\" + \"!\"\n",
    "> ```\n",
    "\n",
    "#### Undefined\n",
    "\n",
    "As $\\mathbf{undefined}$ corresponds to unit `()` in Scala and is\n",
    "uninteresting in itself, we add a side-effecting expression that prints\n",
    "to console.\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{expressions} & e& \\mathrel{::=}& \\texttt{console}\\texttt{.}\\texttt{log}\\texttt{(}e_1\\texttt{)}\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "226c53fa",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">Print</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case class Print(e1: Expr) extends Expr // e ::= console.log(e1)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "afc77e07-23e1-4c34-9f2e-1a4c7c5f5b4e",
   "metadata": {},
   "source": [
    "> **Examples**\n",
    ">\n",
    "> ``` js\n",
    "> console.log(\"Hello, World!\")\n",
    "> ```\n",
    "\n",
    "If we now have side-effecting expressions, then we would expect to have\n",
    "a way to sequence executing expressions for their effects.\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{binary operators} & \\mathit{bop}& \\mathrel{::=}& \\texttt{,}\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "id": "4c211bca",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">object</span> <span class=\"ansi-cyan-fg\">Seq</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case object Seq extends Bop // bop ::= ,"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "579a39c5-348a-46e4-b706-a86e0fbfc617",
   "metadata": {},
   "source": [
    "> **Examples**\n",
    ">\n",
    "> ``` js\n",
    "> undefined, 3\n",
    "> ```\n",
    "\n",
    "### Semantics Detective: JavaScript is Bananas\n",
    "\n",
    "In the above, we have carefully specified the abstract syntax of the\n",
    "object language of interest and informally discussed its semantics. But\n",
    "if we are to implement an interpreter in the `eval` function, we also\n",
    "need to define its semantics! And we give a precise definition as\n",
    "follows:\n",
    "\n",
    "> **Important**\n",
    ">\n",
    "> In this lab, the semantics of a JavaScripty expression $e$ is defined\n",
    "> by the evaluation of it as a JavaScript program.\n",
    "\n",
    "Given the careful specification of the abstract syntax, a natural\n",
    "question to ask is whether all abstract syntax trees of type `Expr` in\n",
    "the above are valid expressions and have a semantics in JavaScript (and\n",
    "hence JavaScripty). Is `3 + true` a valid expression?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "3e3c4c0b-3d04-40c6-b11a-8ab618b54796",
   "metadata": {},
   "outputs": [
    {
     "data": {},
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "3 + true"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "7af09a5d-90d7-4284-b408-51098a6bc898",
   "metadata": {},
   "source": [
    "We try it out and see that yes it is. One aspect that makes the\n",
    "JavaScript specification interesting is the presence of implicit\n",
    "coercions (e.g., non-numeric values, such as booleans or strings, may be\n",
    "implicitly converted to numeric values depending on the context in which\n",
    "they are used).\n",
    "\n",
    "You might guess that defining coercions between value types can lead to\n",
    "some interesting semantics. It is because of these coercions that we\n",
    "have the meme that “JavaScript is bananas.”"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "0bbdf44a-efd4-42e7-ab8b-3e58b85414dd",
   "metadata": {},
   "outputs": [
    {
     "data": {},
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "\"b\" + \"a\" + \"n\" + - \"a\" + \"a\" + \"s\""
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a614770c-4f97-4e4b-8ffa-83c4ee7a535b",
   "metadata": {},
   "source": [
    "Armed with knowledge that in JavaScript, numbers are floating-point\n",
    "numbers, the `+` operator in JavaScript is overloaded for strings and\n",
    "numbers, and coercions happen between value types, see if you can\n",
    "explain what is happening in the “bananas” expression above.\n",
    "\n",
    "#### Coercions\n",
    "\n",
    "Our `eval` function interpreter will need to make use of three helper\n",
    "functions for converting values to numbers, booleans, and strings:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "76e48b08",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">toNumber</span>\n",
       "defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">toBoolean</span>\n",
       "defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">toStr</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def toNumber(v: Expr): Double = ???\n",
    "def toBoolean(v: Expr): Boolean = ???\n",
    "def toStr(v: Expr): String = ???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "877ad7ab-c025-46d1-8597-a2dc7960e167",
   "metadata": {},
   "source": [
    "<span class=\"theorem-title\">**Exercise 2**</span> Write at least 1\n",
    "JavaScript expression that shows a coercion from a non-numeric value to\n",
    "a number and see what the result should be:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "ecf717e2-a8a2-4163-a2fc-626d3c32614c",
   "metadata": {},
   "outputs": [
    {
     "data": {},
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "// YOUR CODE HERE\n",
    "undefined"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "c2e075a3-d8c2-4d4d-b50c-3b05446e7138",
   "metadata": {},
   "source": [
    "Then, translate this JavaScript expression (written in concrete syntax)\n",
    "into an `Expr` value (i.e., a JavaScripty abstract syntax tree)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "id": "f2373c38",
   "metadata": {},
   "outputs": [],
   "source": [
    "???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "15ae65f0-171c-439e-8391-55db52bc29c7",
   "metadata": {},
   "source": [
    "Finally, use this `Expr` as a unit test for `toNumber` in the\n",
    "`Lab2StudentSpec` class in the `Lab2Spec.scala` file.\n",
    "\n",
    "``` scala\n",
    "val e_toNumber_test1 = ???\n",
    "\"toNumber\" should s\"${e_toNumber_test1}\" in {\n",
    "  assertResult(???) { toNumber(e_toNumber_test1) }\n",
    "}\n",
    "```\n",
    "\n",
    "<span class=\"theorem-title\">**Exercise 3**</span> Do the same to create\n",
    "a `toBoolean` test. Write at least 1 JavaScript expression that shows a\n",
    "coercion from a non-boolean value to a boolean, see what the result\n",
    "should be, translate it to an `Expr` value, and add it as test in\n",
    "`Lab2StudentSpec`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2028060d-7a15-4b27-9153-4acb2911dcce",
   "metadata": {},
   "outputs": [
    {
     "data": {},
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "// YOUR CODE HERE\n",
    "undefined"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "id": "2eb72698",
   "metadata": {},
   "outputs": [],
   "source": [
    "???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6e8628d8-49de-4749-8c8c-c3e9a5ae2569",
   "metadata": {},
   "source": [
    "<span class=\"theorem-title\">**Exercise 4**</span> Do the same to create\n",
    "a `toStr` test. Write at least 1 JavaScript expression that shows a\n",
    "coercion from a non-string value to a string, see what the result should\n",
    "be, translate it to an `Expr` value, and add it as test in\n",
    "`Lab2StudentSpec`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "09a51a9d-f222-4462-b99e-2237d3d7e76c",
   "metadata": {},
   "outputs": [
    {
     "data": {},
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "// YOUR CODE HERE\n",
    "undefined"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "id": "2b0d83e9",
   "metadata": {},
   "outputs": [],
   "source": [
    "???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b0804229-2e80-4c50-b10d-45bae14ac467",
   "metadata": {},
   "source": [
    "<span class=\"theorem-title\">**Exercise 5**</span> Implement `toNumber`,\n",
    "`toBoolean`, and `toStr` in `Lab2.scala` (using test-driven development\n",
    "with the test cases you have written above).\n",
    "\n",
    "<span class=\"theorem-title\">**Exercise 6**</span> For this part of the\n",
    "lab, extend your `eval` from\n",
    "<a href=\"#exr-numbers-eval\" class=\"quarto-xref\">Exercise 1</a> for\n",
    "booleans, strings, the undefined value, and printing."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "d4af7b6b",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">eval</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def eval(env: Env, e: Expr): Expr = ???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "59a41a5f-f9c2-472c-a3e8-ed1d1511985c",
   "metadata": {},
   "source": [
    "You still will not use the `env` parameter yet. You again will want to\n",
    "check that your implementation returns JavaScripty values using the\n",
    "latest `isValue`. For example,"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "2913288e",
   "metadata": {},
   "outputs": [],
   "source": [
    "val e_nottrue = Unary(Not, B(true))\n",
    "assert( isValue( eval(empty, e_nottrue) ) )"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "5d9adaaa-44a9-4020-a559-e61e98217282",
   "metadata": {},
   "source": [
    "## Interpreter: JavaScripty Variables\n",
    "\n",
    "The final piece of this lab is to extend our interpreter with variable\n",
    "uses and binding (cf. **?@sec-static-scoping**).\n",
    "\n",
    "$$\n",
    "\\begin{array}{rrrl}\n",
    "\\text{expressions} & e& \\mathrel{::=}& x\\mid\\mathbf{const}\\;x\\;\\texttt{=}\\;e_1\\texttt{;}\\;e_2\n",
    "\\end{array}\n",
    "$$"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "9c0ab5cd",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">Var</span>\n",
       "defined <span class=\"ansi-green-fg\">class</span> <span class=\"ansi-cyan-fg\">ConstDecl</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "case class Var(x: String) extends Expr                           // e ::= x\n",
    "case class ConstDecl(x: String, e1: Expr, e2: Expr) extends Expr //     | const x = e1; e2"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3753b5f9-3d1e-4ef3-9ca6-b016448b3fed",
   "metadata": {},
   "source": [
    "Note that the above is the abstract syntax we consider for `ConstDecl`,\n",
    "which is more flexible the concrete syntax for `const` allowed by\n",
    "JavaScript (cf. )\n",
    "\n",
    "In this lab, we define a value environment as a map from variable names\n",
    "to JavaScripty values, which we represent in Scala as a value of type\n",
    "`Map[String, Expr]`. Note that representing variable names as Scala\n",
    "`String`s here, and it is a representation invariant that the `Expr`s\n",
    "must correspond to JavaScripty values."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "id": "74452c05",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">type</span> <span class=\"ansi-cyan-fg\">Env</span>\n",
       "<span class=\"ansi-cyan-fg\">empty</span>: <span class=\"ansi-green-fg\">Env</span> = <span class=\"ansi-yellow-fg\">Map</span>()\n",
       "defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">lookup</span>\n",
       "defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">extend</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "type Env = Map[String, Expr]\n",
    "val empty: Env = Map.empty\n",
    "\n",
    "def lookup(env: Env, x: String): Expr = env(x)\n",
    "def extend(env: Env, x: String, v: Expr): Env = {\n",
    "  require(isValue(v))\n",
    "  env + (x -> v)\n",
    "}"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "abf51752-104b-4fe7-b3bb-56f2b30c651d",
   "metadata": {},
   "source": [
    "We provide the above value and function bindings to interface with the\n",
    "Scala standard library for `Map[String, Expr]` and maintain this\n",
    "representation invariant. You may use the Scala standard library\n",
    "directly if you wish, but we recommend that you just use these\n",
    "interfaces, as they are all that you need and give you the safety of\n",
    "enforcing the representation invariant. The `empty` value represents an\n",
    "empty value environment, the `lookup` function gets the value bound to\n",
    "the variable named by a given string, and the `extend` function extends\n",
    "a given environment with a new variable binding.\n",
    "\n",
    "<span class=\"theorem-title\">**Exercise 7**</span> For this part of the\n",
    "lab, extend your `eval` from\n",
    "<a href=\"#exr-numbers-eval\" class=\"quarto-xref\">Exercise 1</a> for\n",
    "variable uses (i.e., `Var`) and variable binding (i.e., `ConstDecl`). We\n",
    "suggest you start by adding tests with variables uses and `const`\n",
    "bindings to be able do test-driven development (see below)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "id": "cc90dc11",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<pre>defined <span class=\"ansi-green-fg\">function</span> <span class=\"ansi-cyan-fg\">eval</span></pre>"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "def eval(env: Env, e: Expr): Expr = ???"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "2bb3563b-1d34-4f4b-9feb-2b2c8b6f28df",
   "metadata": {},
   "source": [
    "### Testing\n",
    "\n",
    "In this lab, we have carefully defined the syntax of the JavaScripty\n",
    "variant of interest, and we have defined its semantics to be defined to\n",
    "be the same as JavaScript. Thus, you can write any JavaScript program\n",
    "within the syntax defined above to create test cases for your `eval`\n",
    "function. Any of the above JavaScript examples could be used as test\n",
    "cases. In some cases, you may want to write abstract syntax trees\n",
    "directly in Scala (i.e., values of type `Expr`). In other cases, you can\n",
    "use the provided JavaScripty parser to translate concrete syntax (i.e.,\n",
    "values of type `String`) into abstract syntax (i.e., values of type\n",
    "`Expr`).\n",
    "\n",
    "<span class=\"theorem-title\">**Exercise 8 (Optional)**</span> We give\n",
    "some exercises below to explore this subset of JavaScripty that you can\n",
    "then use as test cases that you add to your `Lab2StudentSpec`.\n",
    "\n",
    "#### Basic Arithmetic Operations"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a2c70244-56b8-4945-b53d-4be38c6ed6e3",
   "metadata": {},
   "source": [
    "This program defines two constants, `x` and `y`, and calculates their\n",
    "sum. It then logs the result `sum` to the console."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "862e000e-d1a1-4a25-b8bb-1983badfb81e",
   "metadata": {},
   "outputs": [],
   "source": [
    "const x = 10;\n",
    "const y = 5;\n",
    "const sum = \n",
    "  // YOUR CODE HERE (replace undefined)\n",
    "  undefined\n",
    ";\n",
    "console.log(sum);"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "5db48d42-a357-4957-bdd2-4436e69d521a",
   "metadata": {},
   "outputs": [],
   "source": [
    "console.assert(sum === 15)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "369b9301-1017-497b-8175-0654a035b32e",
   "metadata": {},
   "source": [
    "#### Conditional Expressions"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b8ae58be-e5bd-4d13-a6eb-6d6fffbd7f2a",
   "metadata": {},
   "outputs": [],
   "source": [
    "const a = 10;\n",
    "const b = 20;\n",
    "const max = \n",
    "  // YOUR CODE HERE (replace undefined)\n",
    "  undefined\n",
    ";"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "fe6cbe1e-fc0b-4965-a09a-38adcee24776",
   "metadata": {},
   "outputs": [],
   "source": [
    "console.assert(max === 20)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "32479c1c-d55e-4d89-a4aa-89f58c7397a3",
   "metadata": {},
   "source": [
    "#### Unary and Binary Operations\n",
    "\n",
    "This program checks if a number is positive using a unary negation `-`\n",
    "and a binary relational operator."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "01bed277-7e0a-4ebb-8f85-3bc60ca4637f",
   "metadata": {},
   "outputs": [],
   "source": [
    "const num = -5;\n",
    "const isPositive =\n",
    "  // YOUR CODE HERE (replace undefined)\n",
    "  undefined\n",
    ";"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2547e992-8b43-4944-bce3-045f9a03807a",
   "metadata": {},
   "outputs": [],
   "source": [
    "console.assert(isPositive === false)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "36cab120-2f06-4f1b-a68a-e51ca556cf97",
   "metadata": {},
   "source": [
    "#### Undefined\n",
    "\n",
    "This program demonstrates the correspondence between `undefined` in\n",
    "JavaScript and `()`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "1896f8d4-2fe1-4204-8405-a1a678c70ffe",
   "metadata": {},
   "outputs": [],
   "source": [
    "const r = console.log(\"Hello\");"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b4138580-25dc-4101-9f30-968ad136a1ee",
   "metadata": {},
   "outputs": [],
   "source": [
    "console.assert(r === undefined)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b97d1faf-fb1f-4626-b1c6-405e1fc11ee8",
   "metadata": {},
   "source": [
    "## Submission\n",
    "\n",
    "If you are a University of Colorado Boulder student, we use Gradescope\n",
    "for assignment submission. In summary,\n",
    "\n",
    "-   [ ] Create a private GitHub repository by clicking on a GitHub\n",
    "    Classroom link from the corresponding Canvas assignment entry.\n",
    "-   [ ] Clone your private GitHub repository to your development\n",
    "    environment (using the `<> Code` button on GitHub to get the\n",
    "    repository URL).\n",
    "-   [ ] Work on this lab from your cloned repository. Use Git to save\n",
    "    versions on GitHub (e.g., `git add`, `git commit`, `git push` on the\n",
    "    command line or via VSCode).\n",
    "-   [ ] Submit to the corresponding Gradescope assignment entry for\n",
    "    grading by choosing GitHub as the submission method.\n",
    "\n",
    "You need to have a GitHub identity and must have your full name in your\n",
    "GitHub profile in case we need to associate you with your submissions."
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Scala",
   "language": "scala",
   "name": "scala"
  },
  "language_info": {
   "codemirror_mode": "text/x-scala",
   "file_extension": ".sc",
   "mimetype": "text/x-scala",
   "name": "scala",
   "nbconvert_exporter": "script",
   "version": "2.13.4"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 5
}