-
Notifications
You must be signed in to change notification settings - Fork 0
/
part1.html
521 lines (485 loc) · 17.5 KB
/
part1.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
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
<title>A Taste of Haskell - Part 1</title>
<meta name="author" content="Sergio de Carvalho">
<link rel="stylesheet" href="css/reveal.css">
<link rel="stylesheet" href="css/theme/moon.css">
<!-- Theme used for syntax highlighting of code -->
<link rel="stylesheet" href="lib/css/zenburn.css">
<!-- Printing and PDF exports -->
<script>
var link = document.createElement( 'link' );
link.rel = 'stylesheet';
link.type = 'text/css';
link.href = window.location.search.match( /print-pdf/gi ) ? 'css/print/pdf.css' : 'css/print/paper.css';
document.getElementsByTagName( 'head' )[0].appendChild( link );
</script>
<!--[if lt IE 9]>
<script src="lib/js/html5shiv.js"></script>
<![endif]-->
</head>
<body>
<div class="reveal">
<div class="slides">
<section>
<h1>A Taste of Haskell</h1>
<h2>Part 1</h2>
</section>
<section>
<h2>Haskell</h2>
<ul>
<li>Modern general-purpose programming language</li>
<li class="fragment">Strong, static type system with type inference</li>
<li class="fragment">Purely functional</li>
<li class="fragment">Non-strict semantics (lazy evaluation)</li>
<li class="fragment">High-performance parallel garbage collector</li>
<li class="fragment">Light-weight concurrency library</li>
<li class="fragment">Free and open</li>
</ul>
</section>
<section>
<h2>Haskell</h2>
<ul>
<li>Created in 1987 to unify several developments on functional programming</li>
<li class="fragment">Named after mathematician Haskell Brooks Curry</li>
<li class="fragment">Current language standard is Haskell 2010</li>
<li class="fragment">The Glasgow Haskell Compiler (<strong>GHC</strong>) is the most commonly used compiler</li>
<li class="fragment"><strong>Stack</strong> is a cross-platform tool for developing, testing, building, Haskell projects</li>
</ul>
</section>
<section>
<h2>Imperative vs. Functional Style</h2>
<p>Imperative
<pre><code class="java" data-trim data-noescape>
int total = 0;
for (int n = 1; n <= 100; n++)
if (n % 2 == 0)
total += n;
</code></pre>
<p>Functional</p>
<pre><code class="haskell" data-trim data-noescape>
total = sum (filter even [1..100])
</code></pre>
</section>
<section>
<h2>Values</h2>
<p>Defined with an equation</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>a = 2</strong>
Prelude> <strong>5 * a</strong>
10
Prelude> <strong>b = 10 * a</strong>
Prelude> <strong>b</strong>
20
Prelude> <strong>c = b < 100</strong>
Prelude> <strong>c</strong>
True
</code></pre>
<p>Values in Haskell are <strong>immutable</strong></p>
</section>
<section>
<h2>Functions</h2>
<p>Defined with an equation, take one or more <strong>parameters</strong></p>
<pre><code class="haskell" data-trim data-noescape>
double x = 2 * x
</code></pre>
<p>Produce single result when applied to arguments</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>double 5</strong>
10
</code></pre>
<p>Function application can be nested</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>double (double 5)</strong>
20
</code></pre>
</section>
<section>
<h2>Function Application</h2>
<p>Parameters and arguments are separated by spaces</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>add x y = x + y</strong>
Prelude> <strong>add 2 5</strong>
7
</code></pre>
<p>Function application has higher priority than other operators so
<strong><code>f a + b</code></strong> means <strong><code>(f a) + b</code></strong>
</p>
<p>Use parantheses to change order of evaluation, e.g.<br>
<strong><code>f (a + b)</code></strong>
</p>
</section>
<section>
<h2>Value, Function and Parameter Names</h2>
<ul>
<li>Must <strong>begin with a lower-case letter</strong></li>
<li>Followed by zero or more:</li>
<ul>
<li>Lower- and upper-case letters</li>
<li>Digits, underscores, and foward single-quotes (<strong><code>'</code></strong>)</li>
</ul>
<li>Valid: <span class="greentext"><code>myFunc</code></span>,
<span class="greentext"><code>arg_1</code></span>,
<span class="greentext"><code>x'</code></span>,
<span class="greentext"><code>x''</code></span>
</li>
<li>Invalid: <span class="redtext"><code>MyFunc</code></span>,
<span class="redtext"><code>1arg</code></span>,
<span class="redtext"><code>'x</code></span>
</li>
</ul>
</section>
<section>
<h2>Basic Types</h2>
<table>
<tbody>
<tr>
<td><strong><code>Bool</code></strong></td>
<td>Logical values</td>
<td><strong><code>True</code></strong> and <strong><code>False</code></strong></td>
</tr>
<tr>
<td><strong><code>Char</code></strong></td>
<td>Single characters</td>
<td><strong><code>'a'</code></strong>, <strong><code>'B'</code></strong>, <strong><code>'1'</code></strong></td>
</tr>
<tr>
<td><strong><code>String</code></strong></td>
<td>List of <code>Chars</code></td>
<td><strong><code>"abc"</code></strong>, <strong><code>""</code></strong>, <strong><code>"a"</code></strong></td>
</tr>
<tr>
<td><strong><code>Int</code></strong></td>
<td>Fixed precision</td>
<td><strong><code>1</code></strong>, <strong><code>-10</code></strong>, <strong><code>999</code></strong></td>
</tr>
<tr>
<td><strong><code>Integer</code></strong></td>
<td>Arbitrary precision</td>
<td><strong><code>99999999999999</code></strong></td>
</tr>
<tr>
<td><strong><code>Float</code></strong></td>
<td>Single precision</td>
<td><strong><code>1.0</code></strong>, <strong><code>-0.99</code></strong></td>
</tr>
<tr>
<td><strong><code>Double</code></strong></td>
<td>Double precision</td>
<td><strong><code>999999999999.9</code></strong></td>
</tr>
</tbody>
</table>
</section>
<section>
<h2>Types</h2>
<p>The notation <strong><code>v :: T</code></strong> indicates
<strong><code>v</code></strong> <em>has type</em>
<strong><code>T</code></strong>
</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:type True</strong>
True :: Bool
Prelude> <strong>:t 'a'</strong>
'a' :: Char
Prelude> <strong>:t "a"</strong>
"a" :: [Char]
</code></pre>
</section>
<section>
<h2>Function Types</h2>
<p>Every expression has a type, including functions</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:type not</strong>
not :: Bool -> Bool
Prelude> <strong>not True</strong>
False
Prelude> <strong>not False</strong>
True
</code></pre>
<p>Functions can be declared with a type</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:{</strong>
Prelude| <strong>happy :: Bool -> Bool -> Bool</strong>
Prelude| <strong>happy sunny cold = sunny && not cold</strong>
Prelude| <strong>:}</strong>
Prelude> <strong>happy True True</strong>
False
Prelude> <strong>happy True False</strong>
True
</code></pre>
</section>
<section>
<h2>Type Inference</h2>
<p>If not declared, types are inferred</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>sad sunny cold = not sunny || cold</strong>
Prelude> <strong>:t sad</strong>
sad :: Bool -> Bool -> Bool
Prelude> <strong>sad True False</strong>
False
Prelude> <strong>double x = x * 2</strong>
Prelude> <strong>:t double</strong>
double :: Num a => a -> a
</code></pre>
<p><strong><code>Num a =></code></strong> is a <em>polymorphic constraint</em></p>
</section>
<section>
<h2>Getting Help in GHCi</h2>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:info Num</strong>
class Num a where
(+) :: a -> a -> a
(-) :: a -> a -> a
(*) :: a -> a -> a
negate :: a -> a
abs :: a -> a
signum :: a -> a
fromInteger :: Integer -> a
{-# MINIMAL (+), (*), abs, signum, fromInteger, (negate | (-)) #-}
instance Num Word -- Defined in ‘GHC.Num’
instance Num Integer -- Defined in ‘GHC.Num’
instance Num Int -- Defined in ‘GHC.Num’
instance Num Float -- Defined in ‘GHC.Float’
instance Num Double -- Defined in ‘GHC.Float’
</code></pre>
</section>
<section>
<h2>Operators Are Functions</h2>
<p>Normally written between two arguments (<strong>infix</strong>)</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t (+)</strong>
(+) :: Num a => a -> a -> a
Prelude> <strong>2 + 5</strong>
7
Prelude> <strong>:t (&&)</strong>
(&&) :: Bool -> Bool -> Bool
Prelude> <strong>True && False</strong>
False
</code></pre>
<p>Can also be used in <strong>prefix</strong> notation using brackets</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>(+) 2 5</strong>
7
Prelude> <strong>(&&) True False</strong>
False
</code></pre>
</section>
<section>
<h2>More Operators</h2>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t (==)</strong>
(==) :: Eq a => a -> a -> Bool
Prelude> <strong>1 == 2</strong>
False
Prelude> <strong>:t (/=)</strong>
(/=) :: Eq a => a -> a -> Bool
Prelude> <strong>1 /= 2</strong>
True
</code></pre>
<p>Functions can be used in <strong>infix</strong> notation using backticks</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t div</strong>
div :: Integral a => a -> a -> a
Prelude> <strong>div 10 3</strong>
3
Prelude> <strong>10 `div` 3</strong>
3
Prelude> <strong>10 `mod` 3</strong>
1
</code></pre>
</section>
<section>
<h2>Working with Negative Numbers</h2>
<p>Binary subtraction operator and <strong><code>negate</code></strong>
function</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t (-)</strong>
(-) :: Num a => a -> a -> a
Prelude> <strong>2 - 1</strong>
1
Prelude> <strong>:t negate</strong>
negate :: Num a => a -> a
Prelude> <strong>negate 1</strong>
-1
</code></pre>
<p>Unary minus is syntatic sugar for <strong><code>negate</code></strong></p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>x = -1</strong>
Prelude> <strong>x</strong>
-1
Prelude> <strong>y = 2 * (-1)</strong>
Prelude> <strong>y</strong>
-2
</code></pre>
</section>
<section>
<h2>Lists</h2>
<p>Sequences of <strong>elements of the same type</strong></p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t [True,False,True]</strong>
[True,False,True] :: [Bool]
Prelude> <strong>:t ['a','b','c']</strong>
['a','b','c'] :: [Char]
Prelude> <strong>:t ["abc","def"]</strong>
["abc","def"] :: [[Char]]
Prelude> <strong>:t []</strong>
[] :: [a]
</code></pre>
<p>The type of a list conveys no information about its length; in fact,
lists can be infinite!
</p>
</section>
<section>
<h2>Working with Lists</h2>
<p>The <strong>cons</strong> (<strong><code>:</code></strong>) and
<strong>concatenation</strong> (<strong><code>++</code></strong>) operators
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t (:)</strong>
(:) :: a -> [a] -> [a]
Prelude> <strong>1 : []</strong>
[1]
Prelude> <strong>1 : [2, 3]</strong>
[1,2,3]
Prelude> <strong>:t (++)</strong>
(++) :: [a] -> [a] -> [a]
Prelude> <strong>[1] ++ [2]</strong>
[1,2]
Prelude> <strong>[1,2] ++ [3,4]</strong>
[1,2,3,4]
Prelude> <strong>[] ++ []</strong>
[]
</code></pre>
</section>
<section>
<h2>Useful List Functions</h2>
<div class="two-columns">
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>head [1,2,3,4,5]</strong>
1
Prelude> <strong>tail [1,2,3,4,5]</strong>
[2,3,4,5]
Prelude> <strong>[1,2,3,4,5] !! 2</strong>
3
Prelude> <strong>take 3 [1,2,3,4,5]</strong>
[1,2,3]
Prelude> <strong>drop 3 [1,2,3,4,5]</strong>
[4,5]
Prelude> <strong>length [1,2,3,4,5]</strong>
5
</code></pre>
</div>
<div class="two-columns">
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>sum [1,2,3,4,5]</strong>
15
Prelude> <strong>product [1,2,3,4,5]</strong>
120
Prelude> <strong>reverse [1,2,3,4,5]</strong>
[5,4,3,2,1]
Prelude> <strong>filter odd [1,2,3,4,5]</strong>
[1,3,5]
Prelude> <strong>null [1]</strong>
False
Prelude> <strong>null []</strong>
True
</code></pre>
</div>
<p><strong>Prelude</strong> is a module containing useful definitions
and functions, included into all Haskell programs by default</p>
</section>
<section>
<h2>Lazy Evaluation</h2>
<p>Expressions are not evaluated until results are needed</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>infinity = [1..]</strong>
Prelude> <strong>take 5 infinity</strong>
[1,2,3,4,5]
Prelude> <strong>take 10 infinity</strong>
[1,2,3,4,5,6,7,8,9,10]
Prelude> <strong>sum (take 1000 (filter even infinity))</strong>
1001000
Prelude> <strong>:t repeat</strong>
repeat :: a -> [a]
Prelude> <strong>repeatedOnes = repeat 1</strong>
Prelude> <strong>take 10 repeatedOnes</strong>
[1,1,1,1,1,1,1,1,1,1]
</code></pre>
<p>It is possible to force the evaluation of an expression, and
Haskell libraries often come with strict variants</p>
</section>
<section>
<h2>Tuples</h2>
<p>Finite sequence of elements of <strong>possibly different types</strong></p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>a = (True, False)</strong>
Prelude> <strong>:t a</strong>
a :: (Bool, Bool)
Prelude> <strong>b = (1, "haskell", not, (True, 'a'))</strong>
Prelude> <strong>:t b</strong>
b :: Num a => (a, [Char], Bool -> Bool, (Bool, Char))
Prelude> <strong>c = ()</strong>
Prelude> <strong>:t c</strong>
c :: ()
Prelude> <strong class="redtext">d = ("tuple of arity one?")</strong>
Prelude> <strong>:t d</strong>
d :: [Char]
</code></pre>
<p>The number of elements in a tuple is called <strong>arity</strong>;
tuples of arity one are not permitted!
</p>
</section>
<section>
<h2>Working with Tuples</h2>
<p>Useful functions for tuples of 2 elements (pairs)</p>
<pre><code class="nohighlight" data-trim data-noescape>
Prelude> <strong>:t fst</strong>
fst :: (a, b) -> a
Prelude> <strong>:t snd</strong>
snd :: (a, b) -> b
Prelude> <strong>fst (1, True)</strong>
1
Prelude> <strong>snd (1, True)</strong>
True </code></pre>
</section>
<section>
<h2>Hoogle</h2>
<ul>
<li>Search Haskell libraries by function name or approximate type signature</li>
<li><a href="https://www.haskell.org/hoogle" target="_blank">www.haskell.org/hoogle</a></li>
<li>Example searches:
<ul>
<li><code><a href="https://www.haskell.org/hoogle/?hoogle=fst" target="_blank">fst</a></code></li>
<li><code><a href="https://www.haskell.org/hoogle/?hoogle=(a%2C+b)+->+a" target="_blank">(a, b) -> a</a></code></li>
</ul>
</li>
</ul>
</section>
<section>
<h2>Exercises</h2>
<p><a href="exercises1.html">Part 1</a></p>
</section>
<section>
<h2>Continue to <a href="part2.html">part 2</a>...</h2>
</section>
</div>
</div>
<script src="lib/js/head.min.js"></script>
<script src="js/reveal.js"></script>
<script>
Reveal.initialize({
transition: 'fade',
history: true,
dependencies: [
{ src: 'plugin/markdown/marked.js' },
{ src: 'plugin/markdown/markdown.js' },
{ src: 'plugin/notes/notes.js', async: true },
{ src: 'plugin/highlight/highlight.js', async: true, callback: function() { hljs.initHighlightingOnLoad(); } }
]
});
</script>
</body>
</html>