![Imperative programming
●
records =
[ "one", "two", "three", "four", "five" ]
filtered = []; j = 0;
for (i = 0; i < length records; i++) {
if (records[i] matches “o”) {
filtered[j++] = records[i];
}
}](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-6-320.jpg)
![Imperative programming
●
records =
[ "one", "two", "three", "four", "five" ]
filtered = []; j = 0;
for (i = 0; i < length records; i++) {
if (records[i] matches “o”) {
filtered[j++] = records[i];
}
}](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-7-320.jpg)
![Your language has this construct
● Perl: my @filtered = grep /o/, @records;
● .Net: var filtered = from r in records
where r.match('o') select r
● Ruby: @filtered = @records.grep /o/
● Python: filtered = [x for x in records
if re.match('o', x)]
● etc.](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-11-320.jpg)
![Quiz data type
●
data QuizNode =
Quiz Name [QuizNode]
| Section Name Score [QuizNode]
| RandomSection Name Score Choose [QuizNode]
| Question Name Score Answer](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-23-320.jpg)
![Quiz data type
●
data QuizNode =
Quiz Name [QuizNode]
| Section Name Score [QuizNode]
| RandomSection Name Score Choose [QuizNode]
| Question Name Score Answer
●
type Name = String
type Score = Int
type Choose = Int](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-24-320.jpg)
![Quiz data type
●
data QuizNode =
Quiz Name [QuizNode]
| Section Name Score [QuizNode]
| RandomSection Name Score Choose [QuizNode]
| Question Name Score Answer
●
data Answer = MultiChoice [BoolAnswer]
| StringChoice [String]](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-25-320.jpg)
![Quiz data type
●
data QuizNode =
Quiz Name [QuizNode]
| Section Name Score [QuizNode]
| RandomSection Name Score Choose [QuizNode]
| Question Name Score Answer
●
data Answer = MultiChoice [BoolAnswer]
| StringChoice [String]
●
data BoolAnswer = BoolAnswer Bool String](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-26-320.jpg)
![Quiz data type
quiz,geo,pop :: QuizNode
quiz = Quiz “General Knowledge Quiz” [ pop, geo ]
geo = RandomSection “Geography” 40 2 [
Question “What is the capital of England?”
2 $ StringChoice [“London”],
Question “What is the capital of France?”
2 $ StringChoice [“Paris”],
Question “What is the capital of Finland?”
2 $ StringChoice [“Helsinki”],
Question “What is the capital of Italy?”
2 $ StringChoice [“Rome”, “Roma”],
]](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-27-320.jpg)
![Quiz data type
quiz,geo,pop :: QuizNode
quiz = Quiz “General Knowledge Quiz” [ pop, geo ]
geo = RandomSection “Geography” 40 2 [
Question “What is the capital of England?”
2 $ StringChoice [“London”],
Question “What is the capital of France?”
2 $ StringChoice [“Paris”],
Question “What is the capital of Finland?”
2 $ StringChoice [“Helsinki”],
Question “What is the capital of Italy?”
2 $ StringChoice [“Rome”, “Roma”],
]](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-28-320.jpg)
![Quiz data type
quiz,geo,pop :: QuizNode
quiz = Quiz “General Knowledge Quiz” [ pop, geo ]
geo = RandomSection “Geography” 40 2 [
Question “What is the capital of England?”
2 $ StringChoice [“London”],
Question “What is the capital of France?”
2 $ StringChoice [“Paris”],
Question “What is the capital of Finland?”
2 $ StringChoice [“Helsinki”],
Question “What is the capital of Italy?”
2 $ StringChoice [“Rome”, “Roma”],
]](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-29-320.jpg)
![Quiz data type
pop = Section “Pop music” 60 [
Question “Which of these are Beatles?” 5
$ MultiChoice [
y “John”,
y “Paul”,
y “George”,
y “Ringo”,
n “Bob”,
n “Jason” ],
...](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-30-320.jpg)
![Quiz data type
pop = Section “Pop music” 60 [
Question “Which of these are Beatles?” 5
$ MultiChoice [
BoolAnswer True “John”,
BoolAnswer True “Paul”,
BoolAnswer True “George”,
BoolAnswer True “Ringo”,
BoolAnswer False “Bob”,
BoolAnswer False “Jason” ],
...](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-31-320.jpg)
![Quiz data type
pop = Section “Pop music” 60 [
Question “Which of these are Beatles?” 5
$ MultiChoice [
y “John”,
y “Paul”,
y “George”,
y “Ringo”,
n “Bob”,
n “Jason” ],
...
y,n :: String -> BoolAnswer
y = BoolAnswer True
n = BoolAnswer False](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-32-320.jpg)
![Taking the quiz!
●
takeNode ::
QuizNode -> IO CompletedNode
●
printQuestion ::
QuizNode -> IO ()
●
showBoolTextAnswers ::
[BoolAnswer] -> String
●
checkAnswer ::
String -> Answer -> Bool](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-58-320.jpg)
![Taking the quiz!
●
takeNode ::
QuizNode -> IO CompletedNode
●
printQuestion ::
QuizNode -> IO ()
●
showBoolTextAnswers ::
[BoolAnswer] -> String
●
checkAnswer ::
String -> Answer -> Bool](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-59-320.jpg)
![Taking the quiz!
●
takeNode ::
QuizNode -> IO CompletedNode
●
printQuestion ::
QuizNode -> IO ()
●
showBoolTextAnswers ::
[BoolAnswer] -> String
●
checkAnswer ::
String -> Answer -> Bool](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-60-320.jpg)
![Taking the quiz!
●
takeNode ::
QuizNode -> IO CompletedNode
●
printQuestion ::
QuizNode -> IO ()
●
showBoolTextAnswers ::
[BoolAnswer] -> String
●
checkAnswer ::
String -> Answer -> Bool](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-61-320.jpg)
![takeNode
takeNode node@(Question s i a) = do
printQuestion node
ans <- getLine
let correct = checkAnswer ans a
let score = if correct
then (i,i) else (0,i)
putStrLn $ if correct
then “Correct!” else “Wrong!”
return $
CompletedNode ans score [] node](https://image.slidesharecdn.com/fptalk-110605060436-phpapp01/85/Haskell-in-the-Real-World-62-320.jpg)
Haskell in the Real World
- 1. Haskell in the Real World Functional Programming Night Geekup Liverpool, 31st May, 2011 [email protected] http://www.fickr.com/photos/jef_saf/3493852795/
- 2. What makes FP different? ● MJD quoting Norvig (on Lisp): ● “big, important features, features like frst-class functions, dynamic access to the symbol table, and automatic storage management.” ● gluing functions together ● declarative
- 3. Popular FP languages ● Excel ● SQL? ● Linq (based on Haskell's monads) ● Lisp → Scheme → Clojure ● Strongly Typed FP (Hindley/Milner) ● ML → Ocaml → F# ● Haskell
- 4. What makes Haskell different? ● Purity ● Laziness ● High Level ● Strong Typing ● Memory Managed ● Modular ● Mathematical rigour ● category theory
- 5. Sounds a bit ivory tower? ● http://prog21.dadgum.com/31.html ● Q “When will Haskell fnally go mainstream?” ● A “most of it already has.”
- 6. Imperative programming ● records = [ "one", "two", "three", "four", "five" ] filtered = []; j = 0; for (i = 0; i < length records; i++) { if (records[i] matches “o”) { filtered[j++] = records[i]; } }
- 7. Imperative programming ● records = [ "one", "two", "three", "four", "five" ] filtered = []; j = 0; for (i = 0; i < length records; i++) { if (records[i] matches “o”) { filtered[j++] = records[i]; } }
- 8. Functional version ● filtered = filter (=~ “o”) records
- 9. Why is this better? ● less code. less bugs ● no synthetic variables ● i, j, length records ● no risk of off-by-one error ● intent clear from skimming ● intent clear to compiler ● parallelize (MapReduce, Hadoop)
- 10. Why is this better? ● fewer codes. fewer bugs ● no synthetic variables ● i, j, length records ● no risk of off-by-one error ● intent clear from skimming ● intent clear to compiler ● parallelize (MapReduce, Hadoop)
- 11. Your language has this construct ● Perl: my @filtered = grep /o/, @records; ● .Net: var filtered = from r in records where r.match('o') select r ● Ruby: @filtered = @records.grep /o/ ● Python: filtered = [x for x in records if re.match('o', x)] ● etc.
- 12. Another example ● countCaps = length . filter (isUpper . head) . words > countCaps “Hello there, Fred” 2
- 13. Real World Haskell ● JSON library ● barcode reading ● database
- 14. Quizzes ● important subsystem of Makini's attention management system ● real world (has customers, pays wages) ● currently written in Perl ● could it be ported to Haskell?
- 15. Haskell Quiz – proof of concept ● full code at: ● https://github.com/ osfameron/geekup-talk-haskell/ ● overview, to give a favour of programming in Haskell
- 22. Quiz tree data types ● Quizzes ● Sections ● (randomized sections) ● Questions
- 23. Quiz data type ● data QuizNode = Quiz Name [QuizNode] | Section Name Score [QuizNode] | RandomSection Name Score Choose [QuizNode] | Question Name Score Answer
- 24. Quiz data type ● data QuizNode = Quiz Name [QuizNode] | Section Name Score [QuizNode] | RandomSection Name Score Choose [QuizNode] | Question Name Score Answer ● type Name = String type Score = Int type Choose = Int
- 25. Quiz data type ● data QuizNode = Quiz Name [QuizNode] | Section Name Score [QuizNode] | RandomSection Name Score Choose [QuizNode] | Question Name Score Answer ● data Answer = MultiChoice [BoolAnswer] | StringChoice [String]
- 26. Quiz data type ● data QuizNode = Quiz Name [QuizNode] | Section Name Score [QuizNode] | RandomSection Name Score Choose [QuizNode] | Question Name Score Answer ● data Answer = MultiChoice [BoolAnswer] | StringChoice [String] ● data BoolAnswer = BoolAnswer Bool String
- 27. Quiz data type quiz,geo,pop :: QuizNode quiz = Quiz “General Knowledge Quiz” [ pop, geo ] geo = RandomSection “Geography” 40 2 [ Question “What is the capital of England?” 2 $ StringChoice [“London”], Question “What is the capital of France?” 2 $ StringChoice [“Paris”], Question “What is the capital of Finland?” 2 $ StringChoice [“Helsinki”], Question “What is the capital of Italy?” 2 $ StringChoice [“Rome”, “Roma”], ]
- 28. Quiz data type quiz,geo,pop :: QuizNode quiz = Quiz “General Knowledge Quiz” [ pop, geo ] geo = RandomSection “Geography” 40 2 [ Question “What is the capital of England?” 2 $ StringChoice [“London”], Question “What is the capital of France?” 2 $ StringChoice [“Paris”], Question “What is the capital of Finland?” 2 $ StringChoice [“Helsinki”], Question “What is the capital of Italy?” 2 $ StringChoice [“Rome”, “Roma”], ]
- 29. Quiz data type quiz,geo,pop :: QuizNode quiz = Quiz “General Knowledge Quiz” [ pop, geo ] geo = RandomSection “Geography” 40 2 [ Question “What is the capital of England?” 2 $ StringChoice [“London”], Question “What is the capital of France?” 2 $ StringChoice [“Paris”], Question “What is the capital of Finland?” 2 $ StringChoice [“Helsinki”], Question “What is the capital of Italy?” 2 $ StringChoice [“Rome”, “Roma”], ]
- 30. Quiz data type pop = Section “Pop music” 60 [ Question “Which of these are Beatles?” 5 $ MultiChoice [ y “John”, y “Paul”, y “George”, y “Ringo”, n “Bob”, n “Jason” ], ...
- 31. Quiz data type pop = Section “Pop music” 60 [ Question “Which of these are Beatles?” 5 $ MultiChoice [ BoolAnswer True “John”, BoolAnswer True “Paul”, BoolAnswer True “George”, BoolAnswer True “Ringo”, BoolAnswer False “Bob”, BoolAnswer False “Jason” ], ...
- 32. Quiz data type pop = Section “Pop music” 60 [ Question “Which of these are Beatles?” 5 $ MultiChoice [ y “John”, y “Paul”, y “George”, y “Ringo”, n “Bob”, n “Jason” ], ... y,n :: String -> BoolAnswer y = BoolAnswer True n = BoolAnswer False
- 33. Stamping the quiz 1x 2x
- 34. Stamping the quiz 1x 2x
- 35. Stamping the quiz stamp :: QuizNode → ... 1x 2x
- 36. Stamping the quiz stamp :: QuizNode → QuizNode? 1x 2x
- 37. Functions ● increment :: Num → Num ● increment 4 => 5 ● increment 10 => 11
- 38. Functions ● increment :: Num → Num ● increment 4 => 5 ● increment 10 => 11
- 39. Functions ● increment :: Num → Num ● increment 4 => 5 ● increment 10 => 11
- 40. Functions ● increment :: Num → Num ● increment x = x+1
- 41. Functions let x = 42 addx :: Num → Num add y = x + y
- 42. Functions (cannot let x = 42 change!) addx :: Num → Num add y = x + y
- 43. Functions let x = 42 addx :: Num → Num add y = x + y
- 44. Stamping the quiz stamp :: QuizNode → QuizNode? 1x 2x
- 45. Stamping the quiz stamp :: QuizNode → QuizNode? 1x 2x
- 46. Stamping the quiz stamp :: QuizNode → IO QuizNode 1x 2x
- 47. Monads ● Useful data-structure ● Lets us model various thing... ● including IO in a pure language ● Concept is a little confusing ● Using them is (mostly) not too bad.
- 48. Stamping the quiz stamp :: QuizNode → IO QuizNode
- 49. Stamping the quiz stamp :: QuizNode → IO QuizNode 1x 2x
- 50. Stamping the quiz stamp :: QuizNode → IO QuizNode 1x 2x
- 51. Stamping the quiz stamp :: QuizNode → IO QuizNode
- 52. Stamping the quiz stamp :: QuizNode → IO QuizNode
- 53. The stamp function stamp :: QuizNode -> IO QuizNode stamp q@(Question _ _ _) = return q stamp (Quiz s ns) = Quiz s <$> mapM stamp ns stamp (Section s i ns) = Section s i <$> mapM stamp ns stamp (RandomSection s i r ns) = do selected <- pickN r ns Section s i <$> mapM stamp selected
- 54. The stamp function stamp :: QuizNode -> IO QuizNode stamp q@(Question _ _ _) = return q stamp (Quiz s ns) = Quiz s <$> mapM stamp ns stamp (Section s i ns) = Section s i <$> mapM stamp ns stamp (RandomSection s i r ns) = do selected <- pickN r ns Section s i <$> mapM stamp selected
- 55. The stamp function map stamp ns stamp :: QuizNode -> IO QuizNode – “stamp all the child nodes in stamp q@(Question _ _ _) = return q turn” stamp (Quiz s ns) = Quiz s <$> mapM stamp ns stamp (Section s i ns) = Section s i <$> mapM stamp ns stamp (RandomSection s i r ns) = do selected <- pickN r ns Section s i <$> mapM stamp selected
- 56. The stamp function stamp :: QuizNode -> IO QuizNode stamp q@(Question _ _ _) = return q stamp (Quiz s ns) = Quiz s <$> mapM stamp ns stamp (Section s i ns) = Section s i <$> mapM stamp ns stamp (RandomSection s i r ns) = do selected <- pickN r ns Section s i <$> mapM stamp selected
- 57. The stamp function stamp :: QuizNode -> IO QuizNode stamp q@(Question _ _ _) = return q stamp (Quiz s ns) = Quiz s <$> mapM stamp ns stamp (Section s i ns) = Section s i <$> mapM stamp ns stamp (RandomSection s i r ns) = do selected <- pickN r ns Section s i <$> mapM stamp selected 1x
- 58. Taking the quiz! ● takeNode :: QuizNode -> IO CompletedNode ● printQuestion :: QuizNode -> IO () ● showBoolTextAnswers :: [BoolAnswer] -> String ● checkAnswer :: String -> Answer -> Bool
- 59. Taking the quiz! ● takeNode :: QuizNode -> IO CompletedNode ● printQuestion :: QuizNode -> IO () ● showBoolTextAnswers :: [BoolAnswer] -> String ● checkAnswer :: String -> Answer -> Bool
- 60. Taking the quiz! ● takeNode :: QuizNode -> IO CompletedNode ● printQuestion :: QuizNode -> IO () ● showBoolTextAnswers :: [BoolAnswer] -> String ● checkAnswer :: String -> Answer -> Bool
- 61. Taking the quiz! ● takeNode :: QuizNode -> IO CompletedNode ● printQuestion :: QuizNode -> IO () ● showBoolTextAnswers :: [BoolAnswer] -> String ● checkAnswer :: String -> Answer -> Bool
- 62. takeNode takeNode node@(Question s i a) = do printQuestion node ans <- getLine let correct = checkAnswer ans a let score = if correct then (i,i) else (0,i) putStrLn $ if correct then “Correct!” else “Wrong!” return $ CompletedNode ans score [] node
- 63. main main :: IO () main = stamp quiz >>= takeQuiz Function, not entrypoint
- 64. main main :: IO () main = stamp quiz >>= takeQuiz Live Demo!
- 65. Should you go Haskell? ● Power ● Speed? ● can be faster than C (supercompilation) ● can be tricky to optimize ● Jobs? ● In NorthWestUK? ● Libraries & Tools ● Haskell Platform. Hackage. Cabal
- 66. Should you learn Haskell? ● Powerful ● Interesting techniques ● … and ways of thinking about problems ● Ready for future shift to FP ● … possibly in your own language
- 67. Thank you! Questions? ● full code at: ● https://github.com/ osfameron/geekup-talk-haskell/ ● [email protected] http://www.fickr.com/photos/jef_saf/3493852795/