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hammerStream = (element, event, opts = {}) ->
  Bacon.fromBinder (sink) ->
    push = (event) -> sink event
    Hammer(element, opts).on event, push
    -> Hammer(element, opts).off event, push

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data Axis = X | Y | Z

data Cube f = Cube { front, back, left, right, top, bottom :: f }

rotate90 :: Axis -> Cube f -> Cube f
rotate90 X c = c { front  = bottom c
                 , back   = top    c
                 , top    = front  c
                 , bottom = back   c }
rotate90 Y c = c { left   = back   c

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instance Rotational (Cube f) where
  rotate90 X c = c { front  = bottom c
                   , back   = top    c
                   , top    = front  c
                   , bottom = back   c }
  rotate90 Y c = c { left   = back   c
                   , front  = left   c
                   , right  = front  c
                   , back   = right  c }
  rotate90 Z c = c { top    = left   c

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module WhatWhat 
( lol
, cat 
) where
  
lol = 1
cat = 2
coc = 3
suc = 4

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Miten funktio on funktori Haskellissa?

Alla on kirjoitettu auki Learnyouahaskell.comin Functors redux -osiota.

Funktiotyypit

Haskellissa funktiotyyppejä luodaan tyyppikonstruktorilla (->) t1 t2 eli infix-notaatiolla t1 -> t2. Kun kiinnitetään ensimmäinen tyyppiparametri t1, saadaan tyyppikonstruktori (->) t1, joka ottaa vielä täsmälleen yhden tyyppiparametrin.

Funktio funktoriksi

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import Data.Char

main = print (filter isUpperOrLower chars) where 
  chars = "123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz"
  oegy combinator fs x = foldl1 combinator (map ($ x) fs)
  isUpperOrLower = oegy (||) [isUpper, isLower, isDigit]

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import Data.Char

main = print (filter isUpperOrLower chars) where 
  chars = "123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz"
  oegy combinator f1 f2 x = combinator (f1 x) (f2 x)
  isUpperOrLower = oegy (||) isUpper isLower

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import Control.Monad

data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a) deriving Show

jakub = Node (Node (Leaf "Pentti")
                   "Jorma" 
                   (Leaf "Maija")) 
             "Jakub" 
             (Node (Leaf "Jozef") 
                   "Teresa" 

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main = do putStrLn "I need your clothes, boots and SSN:"  
          ssn <- getLine  
          putStrLn (show (isSSN ssn))
          
isSSN ssn = True

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main = do putStrLn "I need your clothes, boots and SSN:"  
          ssn <- getLine  
          putStrLn $ show $ isSSN ssn
          
isSSN ssn = True