howtohaskell

8/6/2019 howtohaskell

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How to Haskelligorgue.com

Saturday, August 6, 11


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MePerson | Programmer | Politics Junky | Hipster Music



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Programming LanguagesNERD



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What is Haskell?



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A standardized, general-purpose purely functionalprogramming language, with non-strict semanticsand strong static typing.

http://en.wikipedia.org/wiki/Type_system#Static_typinghttp://en.wikipedia.org/wiki/Type_system#Static_typinghttp://en.wikipedia.org/wiki/Strong_typinghttp://en.wikipedia.org/wiki/Strong_typinghttp://en.wikipedia.org/wiki/Non-strict_semanticshttp://en.wikipedia.org/wiki/Non-strict_semanticshttp://en.wikipedia.org/wiki/Programming_languagehttp://en.wikipedia.org/wiki/Programming_languagehttp://en.wikipedia.org/wiki/Purely_functionalhttp://en.wikipedia.org/wiki/Purely_functional


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Hello, World!

main = print "Hello, World!"



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A Formal Hello

-- hello.hs: Saying "Hello, World!"module Mainwhere

main :: IO ()

main = putStrLn "Hello, World!"



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Whats FunctionalProgramming?



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Wait... Whats aFunction?



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A function, in mathematics, associates one

quantity, the argumentof the function, also known asthe input, with another quantity, the value of thefunction, also known as the output.

http://en.wikipedia.org/wiki/Mathematicshttp://en.wikipedia.org/wiki/Mathematics


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Pure Functional Programming follows the same

definition as in mathematics. A function will outputthe same value if the same input is passed to it.



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And a functional

programming languageis?



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A programming language

where functions arefirst-class citizens



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Cool Haskell Stuff



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The only one purefunctional programming

languagehttp://www.youtube.com/watch?v=UuamC0T3hv8

http://www.youtube.com/watch?v=UuamC0T3hv8http://www.youtube.com/watch?v=UuamC0T3hv8


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No Side-Effects! YAY!



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A Side Effect

deffunction(y):

return y + x

x = 1print function(1) # => 2

x += 1print function(1) # => 3



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Haskell Turn!

function y = y + x

x =1

function 1-- 2 (This wont be executed by the compiler)

x = x +1 -- SYNTAX ERROR!

function 1-- 3 (This will never happen)



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Lazy Evaluation



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Python vs Haskellprintrange(1, 10000000)[:3] # Python

print(take 3 [1..10000000]) -- Haskell

python range_of_10_mm.py 0.59s user 0.38s system 97% cpu 0.996 total

runhaskell range_of_10_mm.hs 0.21s user 0.04s system 90% cpu 0.270 total

print (take 3 [1..1000000000000000000000000000000]) -- Haskell

runhaskell range_of_many_mm.hs 0.21s user 0.04s system 92% cpu 0.271 total



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Haskell is Dynamic Too!



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string ="foobar"integer =10float =5.34

main =doputStrLn ("String: "++ string)putStrLn ("Integer: "++ show integer)

putStrLn ("Float: "++ show float)



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But, Its Still StronglyTyped!



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string :: Stringstring ="foobar"

integer :: Intinteger =10

float :: Floatfloat =5.34

main :: IO ()

main =doputStrLn ("String: "++ string)putStrLn ("Integer: "++ show integer)putStrLn ("Float: "++ show float)



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My Recent ProblemImplementation of

in_groups_ofI solved it with Haskell... kinda



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Problem

Given a list of n return a list of lists of x size. e.g.:

in_groups_of2 [1, 2, 3, 4, 5, 6]

[[1, 2], [3, 4], [5, 6]]



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# File activesupport/lib/active_support/core_ext/array/grouping.rb, line

22

defin_groups_of(number, fill_with = nil) if fill_with == false

collection = self else

# size % number gives how many extra we have; # subtracting from number gives how many to add; # modulo number ensures we don't add group of just fill.

padding = (number - size % number) % numbercollection = dup.concat([fill_with] * padding)

end

if block_given?collection.each_slice(number) { |slice| yield(slice) }

elsereturning [] do |groups|collection.each_slice(number) { |group| groups


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Haskell Turn!

inGroupsOf :: [a] -> Int -> [[a]]inGroupsOf [] _= []inGroupsOf xs n = let (ys, zs) = splitAt n xs

in ys : inGroupsOf zs n



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Write Web Apps with

it!

http://snapframework.com/

http://snapframework.com/http://snapframework.com/


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igorPage :: Application ()igorPage =do

message


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Why Haskell?



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BECAUSE HASKELL IS

FUN!!!Thanks!

http://igorgue.com/presentations/howtohaskell.pdf
http://igorgue.com/presentations/howtohaskell.pdfhttp://igorgue.com/presentations/howtohaskell.pdf

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