-
Notifications
You must be signed in to change notification settings - Fork 2
/
afp.html
871 lines (614 loc) · 18.3 KB
/
afp.html
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
<!DOCTYPE html>
<html>
<head>
<title>Haskell - The Legend of DSLs</title>
<meta charset="utf-8">
<style>
/* @import url(https://fonts.googleapis.com/css?family=Yanone+Kaffeesatz);
@import url(https://fonts.googleapis.com/css?family=Droid+Serif:400,700,400italic);
@import url(https://fonts.googleapis.com/css?family=Ubuntu+Mono:400,700,400italic); */
@import url(css/metropolis.css);
</style>
</head>
<body>
<textarea id="source">
class: center, middle, title-slide
count: false
.less-line-height[
Alejandro Serrano @ AFP Summer School 2022
.grey[🐦 @trupill - 🐈⬛ serras - 👨💻 47 Degrees]
]
---
# 🥅 Overall goal
### .grey[How do we build software with Haskell?]
---
# 🥅 Overall goal
### .grey[How do we build software with Haskell?]
1. Domain-specific languages <br /> Representing actions and scripts <br /> Property-based testing
2. Communicating over the network <br /> Serialization (without boilerplate) <br /> Error handling <br /> Concurrency across threads
---
# 🥅 Overall goal
### .grey[How do we build software with Haskell?]
1. **Domain-specific languages** <br /> **Representing actions and scripts** <br /> **Property-based testing**
2. Communicating over the network <br /> Serialization (without boilerplate) <br /> Error handling <br /> Concurrency across threads
---
# <img src="img/pikachu.png" width="32px" /> Pokémon Trading Card Game
Players take turns drawing and playing cards
<table>
<tr>
<td style="vertical-align: top"><img src="img/pikachucard.png" width="100%" /></td>
<td width="68%" style="padding-left: 20px; line-height: 1.3;">
<div style="margin-bottom: -20px">Goal: knock out 6 of your opponent's Pokémon</div>
<ul>
<li>For this your use <b>attacks</b></li>
<li>Those attacks cost <b>energy</b></li>
<li>Each attack does <b>damage</b></li>
<li><b>HP</b> define the maximum damage before knock-out</li>
</ul>
</td>
</tr>
</table>
---
# 🏗️ Our approach
### .grey[Explanations interleaved with tasks]
1. Representing cards
2. Representing actions
3. Testing actions
---
# 🏗️ Our approach
### .grey[Explanations interleaved with tasks]
1. Representing cards
2. Representing actions
3. Testing actions
## .grey[Domain-specific Language (DSL)]
Implementation of the _Ubiquitous Language_ idea from DDD, the code speaks the domain
---
# <img src="img/pikachu.png" width="32px" /> Representing cards
<table>
<tr>
<td style="vertical-align: top"><img src="img/pikachucard.png" width="100%" /></td>
<td width="68%" style="padding-left: 20px; line-height: 1.3;">
<div style="margin-bottom: -20px">Each card comes with...</div>
<ul style="margin-bottom: 20px">
<li>Name: <span class="remark-code-zoom">Pikachu</span></li>
<li>Type: <img src="img/energy/lightning.webp" height="32px" /></li>
<li>HP: 70</li>
<li>Attack(s)</li>
</ul>
(forget about the rest for now)
</td>
</tr>
</table>
---
# ⚙️ Algebraic Data Types (ADTs)
<table style="font-size: 70%">
<tr>
<td style="vertical-align: top; text-align: right;"><img src="img/pikachucard.png" width="60%" /></td>
<td width="68%" style="padding-left: 20px; line-height: 1.3;">
<div style="margin-bottom: -20px">Each card comes with...</div>
<ul style="margin-bottom: 20px">
<li>Name: <span class="remark-code-zoom">Pikachu</span></li>
<li>Type: <img src="img/energy/lightning.webp" height="20px" /></li>
<li>HP: 70</li>
<li>Attack(s)</li>
</ul>
</td>
</tr>
</table>
Straightforward translation of the description
.code70[
```haskell
data Card = Card { name :: Text
, typ :: Energy
, hp :: Natural
, attacks :: [Attack] }
```
]
---
# ⚙️ Algebraic Data Types (ADTs)
<table style="font-size: 70%">
<tr>
<td style="vertical-align: top; text-align: right;"><img src="img/pikachucard.png" width="60%" /></td>
<td width="68%" style="padding-left: 20px; line-height: 1.3;">
<div style="margin-bottom: -20px">Each card comes with...</div>
<ul style="margin-bottom: 20px">
<li>Name: <span class="remark-code-zoom">Pikachu</span></li>
<li>Type: <img src="img/energy/lightning.webp" height="20px" /></li>
<li>HP: 70</li>
<li>Attack(s)</li>
</ul>
</td>
</tr>
</table>
.code70[
```haskell
data Card = Card { name :: Text
, typ :: Energy
, hp :: HP
, attacks :: [Attack] }
newtype HP = HP Natural
deriving (Eq, Show, Num)
```
]
---
# ☯️ Energies
There are 10 types of energy in the game,
- 9 regular energies <img src="img/energy/grass.webp" width="32px" /> <img src="img/energy/fire.png" width="32px" /> <img src="img/energy/water.webp" width="32px" /> <img src="img/energy/lightning.webp" width="32px" /> <img src="img/energy/fighting.webp" width="32px" /> <img src="img/energy/psychic.webp" width="32px" /> <img src="img/energy/darkness.webp" width="32px" /> <img src="img/energy/metal.webp" width="32px" /> <img src="img/energy/dragon.webp" width="32px" />
- Colorless energy <img src="img/energy/colorless.webp" width="32px" />
- Any card providing a regular energy may also provide colorless energy
<img src="img/attack.png" height="48px" style="margin-top: 10px; margin-bottom: -10px;" /> = 2 <img src="img/energy/lightning.webp" width="32px" /> + 1 of any other
---
# ☯️ Energies
There are 10 types of energy in the game,
- 9 regular energies <img src="img/energy/grass.webp" width="32px" /> <img src="img/energy/fire.png" width="32px" /> <img src="img/energy/water.webp" width="32px" /> <img src="img/energy/lightning.webp" width="32px" /> <img src="img/energy/fighting.webp" width="32px" /> <img src="img/energy/psychic.webp" width="32px" /> <img src="img/energy/darkness.webp" width="32px" /> <img src="img/energy/metal.webp" width="32px" /> <img src="img/energy/dragon.webp" width="32px" />
- Colorless energy <img src="img/energy/colorless.webp" width="32px" />
.code70[
```haskell
data Energy = Colorless
| Grass | Fire | Water
| Lightning | Fighting | Psychic
| Darkness | Metal | Dragon
data Card = PokemonCard { ... }
| EnergyCard { typ :: Energy }
```
]
---
# ⚔️ Attacks
We consider only "simple" attacks for now
<div style="text-align: center"><img src="img/attack.png" height="60px" /></div>
.code70[
```haskell
data Attack = Attack { attackName :: Text
, cost :: [Energy]
, damage :: Natural }
```
]
---
# 🧑💻 Time for practice!
.very-little-margin-top[
### `serras.github.io/zurihac-workshop`
]
Define values for the following cards
<div style="margin-top: -20px">
<img src="img/grookeycard.png" width="40%" />
<img src="img/goomycard.png" width="40%" />
</div>
---
# 🧑💻 Time for practice!
.very-little-margin-top[
### `serras.github.io/zurihac-workshop`
]
Check whether some energy cards are enough to "pay" for the cost of an attack
```haskell
enoughEnergy :: [Energy] -> [Card] -> Bool
```
Then, refine it to return the missing energy
```haskell
missingEnergy :: [Energy] -> [Card]
-> Maybe [Energy]
```
---
# ⚔️ Attacks, redux
.code70[
```haskell
data Attack = Attack { ..., damage :: Natural }
```
]
## .grey[This is a ~~lie~~ simplification]
---
# ⚔️ Attacks, redux
<img src="img/attack1.png" width="80%" />
<img src="img/attack2.png" width="80%" />
<img src="img/attack3.png" width="80%" />
<img src="img/attack4.png" width="80%" />
---
# ⚔️ Attacks, redux
.code70[
```haskell
data Attack = Attack { ..., damage :: Natural }
```
]
## .grey[This is a ~~lie~~ simplification]
.top-margin[
- More actions than mere damage
- Draw and discard cards
- Actions may depend on the state
- Attached cards
- Coin flips
- Actions may involve conditionals and loops
]
---
# ⚔️ Attacks, redux
.code70[
```haskell
data Attack = Attack { ..., action :: ??? }
```
]
## How do we model .grey[actions]?
.top-margin[
- More actions than mere damage
- Draw and discard cards
- Actions may depend on the state
- Attached cards
- Coin flips
- Actions may involve conditionals and loops
]
---
# 🪙 Coin flips
<img src="img/attack5.png" width="80%" />
.code70[
```haskell
data FlipOutcome = Heads | Tails
data Action
= FlipCoin (FlipOutcome -> Action)
| Damage Natural
surpriseAttackAction
= FlipCoin $ \case Heads -> Damage 30
Tails -> Damage 0
```
]
---
# 🪙 Coin flips
<img src="img/attack1.png" width="80%" />
## .grey[🧑💻 Time for practice!] .font50[`serras.github.io/zurihac-workshop`]
---
# 🪙 Coin flips
<img src="img/attack1.png" width="80%" />
```haskell
ironTailAction = go 0
where
go acc = FlipCoin $ \case
Tails -> Damage acc
Heads -> go (acc + 30)
```
---
# 🧞 Syntax/algebra and interpretation
`Action` defines the **syntax** of our DSL <br /> (also known as **algebra** in some circles)
> "The language itself", "what we can say"
---
# 🧞 Syntax/algebra and interpretation
`Action` defines the **syntax** of our DSL <br /> (also known as **algebra** in some circles)
An **interpretation** defines how each value behaves in a certain context
> "What a sentence means"
1 syntax / algebra ⟷ ∞ interpretations
---
# 🎰 Randomness interpretation
During the actual game, we expect to generate random coin flips to obtain the actual damage
```haskell
interpretRandom :: Action -> IO Natural
```
## .grey[🧑💻 Time for practice!] .font50[`serras.github.io/zurihac-workshop`]
---
# 🎰 Randomness interpretation
During the actual game, we expect to generate random coin flips to obtain the actual damage
```haskell
interpretRandom :: Action -> IO Natural
interpretRandom (Damage d) = pure d
interpretRandom (FlipCoin f) = do
outcome <- flipCoin
interpretRandom (f outcome)
-- one-liner
-- flipCoin >>= interpretRandom . f
```
---
# 🎴 Actions about cards
<img src="img/attack2.png" width="80%" />
<img src="img/attack3.png" width="80%" />
<img src="img/attack4.png" width="80%" />
---
# 🎴 Actions about cards
.code70[
```haskell
data Action
= FlipCoin (FlipOutcome -> Action)
| DrawCard (Maybe Card -> Action)
-- ^ there may not be more cards
| QueryAttached ([Card] -> Action)
-- ^ get info. about the current Pokémon
| Damage Natural
```
]
### .grey[Can you spot the pattern? 🔍]
---
# 🎴 Actions about cards
.code70[
```haskell
data Action
= FlipCoin (FlipOutcome -> Action)
| DrawCard (Maybe Card -> Action)
-- ^ there may not be more cards
| QueryAttached ([Card] -> Action)
-- ^ get info. about the current Pokémon
| Damage Natural
```
]
- `Damage` is a **final** action
- The rest "generate" a value, <br /> which is consumed to keep going
---
# 🔩 The `Operational` monad
.code70[
```haskell
data Program instr a where
Done :: a -> Program instr a
(:>>=) :: instr a
-> (a -> Program instr b)
-> Program instr b
```
]
Split the pattern from the concrete instructions
.code70[
```haskell
data Action a where
FlipCoin :: Action FlipOutcome
DrawCard :: Action (Maybe Card)
QueryAttached :: Action [Card]
```
]
---
# ⚙️ Generalized ADTs (GADTs)
Refine the resulting type from constructors
.code70[
```haskell
{-# language GADTs #-}
data Action a where
FlipCoin :: Action FlipOutcome
DrawCard :: Action (Maybe Card)
QueryAttached :: Action [Card]
```
]
Here `a` represents the "generated" value
---
# 🔩 The `Operational` monad
## .grey[🧑💻 Time for practice!]
.code70[
```haskell
data Program instr a where
Done :: a -> Program instr a
(:>>=) :: instr a
-> (a -> Program instr b)
-> Program instr b
```
Implement the following instances
.little-margin-top[
```haskell
instance Functor (Program instr)
instance Applicative (Program instr)
instance Monad (Program instr)
```
]
]
---
# 🪙 Operational coin flips
<img src="img/attack1.png" width="80%" />
```haskell
perform :: instr a -> Program instr a
perform action = action :>>= Done
instance Functor (Program instr)
instance Applicative (Program instr)
instance Monad (Program instr)
```
---
# 🪙 Operational coin flips
<img src="img/attack1.png" width="80%" />
```haskell
ironTailAction :: Program Action Natural
ironTailAction = do
outcome <- perform FlipCoin
case outcome of
Tails -> pure 0
Heads -> (30 +) <$> ironTailAction
```
---
# 🪙 Operational coin flips
<img src="img/attack1.png" width="80%" />
Being a `Monad` gives access to many functions
.code70[
```haskell
ironTailAction :: Program Action Natural
ironTailAction = do
hs <- unfoldWhileM (== Heads) (perform FlipCoin)
pure $ 30 * genericLength hs
```
]
`unfoldWhileM` comes from `monad-loops`
---
# 🎴 Actions about cards
<img src="img/attack4.png" width="80%" />
## .grey[🧑💻 Time for practice!] .font50[`serras.github.io/zurihac-workshop`]
.margin-top[
1. Write a function to **draw *n* ** cards
2. Add an additional operation to **discard** cards
- Must include a predicate to select cards
- Outcome: whether a card was discarded
]
---
# 🔩 Interpreting `Operational`
One generic function for every `Program`
.code70[
```haskell
interpret :: Monad m
=> (forall x. instr x -> m x)
-- ^ instruction interpreter
-> Program instr a -> m a
interpret f = go
where go (Done x) = return x
go (action :>>= k) = do
x <- f action
go (k x)
-- f action >>= go . k
```
]
---
# 🔩 Interpreting `Operational`
We can focus on each instruction, <br />
instead of dealing with passing information
.code70[
```haskell
interpretRandom :: Program Action a -> IO a
interpretRandom = interpret $ \case
FlipCoin -> flipCoin
-- rest of cases
```
]
---
# 🩻 Property-based testing
Generate many _random_ tests for the same function (or set of them)
Focus on **properties** rather than examples
- PBT frameworks are good at generating corner cases (extreme values, empty lists, ...)
---
# ✅ Testing actions
### .grey[How can we test `ironTailAction`?]
<img src="img/attack1.png" width="80%" />
---
# ✅ Testing actions
### .grey[How can we test `ironTailAction`?]
<img src="img/attack1.png" width="80%" />
- If we get a tail as first result, we get 0
- If our outcomes start with `n` heads, <br /> then the result is `30 * n`
- Both implementations should coincide
---
# ✅ Testing actions
### .grey[How can we test `ironTailAction`?]
<img src="img/attack1.png" width="80%" />
❌ Using `interpretRandom` would not work
- The outcome is random
- Testing `IO` is cumbersome
---
# 🧮 Pure interpretation of flipping
We pass the future outcomes as a parameter
```haskell
interpretPure :: [FlipOutcome]
-> Program Action a -> a
```
---
# 🧮 Pure interpretation of flipping
We pass the future outcomes as a parameter
```haskell
interpretPure :: [FlipOutcome]
-> Program Action a -> a
```
Now we control the future 🔮
```haskell
> interpretPure [Heads, Heads, Tails]
ironTailAction
60
```
---
# 🧮 Pure interpretation of flipping
The `State` monad threads the current value
.code70[
```haskell
interpretPure :: [FlipOutcome]
-> Program Action a -> a
interpretPure outcomes =
flip evalState (cycle outcomes) . interpret f
where f :: Action x -> State [FlipOutcome] x
f FlipCoin = do
~(result : nexts) <- get
put nexts
return result
```
]
---
# 🧮 Pure interpretation of flipping
Writing it by hand might be easier... 🤔
.code70[
```haskell
interpretPure :: [FlipOutcome]
-> Program Action a -> a
interpretPure outcomes = go (cycle outcomes)
where go :: [FlipOutcome]
-> Program Action x -> x
go _ (Done x) = x
go ~(result : nexts) (FlipCoin :>>= k) =
go nexts (k result)
```
]
---
# 🏃 QuickCheck + Tasty 🥧
**QuickCheck** is a well-known library for property-based testing
- Define properties of functions
- Support for custom generators
**Tasty** is a test runner
- Runs and reports over a set of tests
---
# 🏃 QuickCheck + Tasty 🥧
🥧 `testGroup` + 🏃 `testProperty`
- `outcomes` is randomly selected
.code70[
```haskell
tests :: TestTree
tests = testGroup "Iron Tail"
[ testProperty "non-negative" $ \outcomes ->
interpretPure (outcomes ++ [Tails])
ironTailAction >= 0
, ... ]
```
]
---
# ✋ A wrong property
```haskell
interpretPure ... ironTailAction > 0
```
A counter-example is found by QuickCheck
.code70[
```
Iron Tail
non-negative: FAIL
*** Failed! Falsified (after 1 test):
[]
Use --quickcheck-replay=139730 to reproduce.
Use -p '/non-negative/' to rerun this test only.
```
]
---
# <img src="img/pikachu.png" width="32px" /> The "times 30" property
To create good properties you must...
- Be creative with the inputs
- Ensure that inputs are correct
.code70[
```haskell
testProperty "30 * # heads" $ \(hs :: Int) ->
hs > 0 ==>
let outcomes = replicate hs Heads ++ [Tails]
in interpretPure outcomes ironTailAction
== fromIntegral (hs * 30)
```]
---
# ✅ Testing actions
### .grey[🧑💻 Time for practice!] .font50[`serras.github.io/zurihac-workshop`]
<img src="img/attack1.png" width="80%" />
- If we get a tail as first result, we get 0
- Both implementations should coincide
- ...
---
# 📋 Summary
### .grey[Haskell is a great language for DSLs]
.margin-top[
- ADTs model the domain sharply
- We can model both data and processes
- `Operational` save lots of boilerplate
- One model, many interpretations
- Useful for (property-based) testing
]
---
# ↔️ Initial and final style
**Initial** style: modeling actions using `data`
- Variations: direct, free, operational
**Final** style: modeling actions using `class`
- Interpretations represented by `instance`s
- Closer to `interface`s in other languages
---
class: center, middle, title-slide
# 🤩 It's been a pleasure
## Go and tell everybody about Haskell!
</textarea>
<script src="https://remarkjs.com/downloads/remark-latest.min.js">
</script>
<script>
var slideshow = remark.create();
</script>
</body>
</html>