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@gja /basics-1.hs Secret
Last active Jan 4, 2016

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Hydra Implementation in Haskell
let firstArray = 0:1:[2, 3]
-- [0, 1, 2, 3]
let infiniteOnes = 1:infiniteOnes
-- [1, 1, 1, 1, 1, ........................]
-- never stops, hit ctrl-C to get your interpreter back
sumOfElements [] = 0
sumOfElements (x:xs) = x + sumOfElements xs
[1] ++ [3] -- [1, 3]
null [] -- True
null [1] -- False
replicate 2 3 -- [3, 3]
chop [] = []
chop (1:xs) = xs
chop (n:xs) = (replicate (n - 1) (n - 1)) ++ xs
----------------------------------------------------
chop [1]
-- []
chop [4]
-- [3, 3, 3]
chop [3, 3, 3]
-- [2, 2, 3, 3]
chop [9,9,9,9,9,9,9,9,9]
-- [8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9]
countOfChops heads = length (repeatedlyChopTillDead heads)
--------------------------------------------------
countOfChops [1] -- 1
countOfChops [3] -- 5
countOfChops [9,9,9,9,9,9,9,9,9] -- 986409 (this takes a while)
willHerculesDie n heads = any (> n) (map length (repeatedlyChopTillDead heads))
----------------------------------------------------------------------------
willHerculesDie 37 [9,9,9,9,9,9,9,9,9] -- False
willHerculesDie 36 [9,9,9,9,9,9,9,9,9] -- True
-- To load this, save this as hydra.hs
-- then run ghci, and type :l hydra (colon ell hydra)
module Hydra where
firstArray = 0:1:[2, 3]
infiniteOnes = 1:infiniteOnes
chop [] = []
chop (1:xs) = xs
chop (n:xs) = (replicate (n - 1) (n - 1)) ++ xs
-- repeatedlyChop heads = heads:repeatedlyChop (chop heads)
-- takeWhileAlive (x:xs) = if null x then [] else x:(takeWhileAlive xs)
-- repeatedlyChopTillDead heads = takeWhileAlive (repeatedlyChop heads)
repeatedlyChopTillDead heads = takeWhile (not.null) (iterate chop heads)
countOfChops heads = length (repeatedlyChopTillDead heads)
willHerculesDie n heads = any (> n) (map length (repeatedlyChopTillDead heads))
repeatedlyChopTillDead heads = takeWhileAlive (repeatedlyChopTillDead heads)
----------------------------------------------------------------------------
repeatedlyChopTillDead [4]
-- [[4],[3,3,3],[2,2,3,3],[1,2,3,3],[2,3,3],[1,3,3],[3,3],[2,2,3],[1,2,3],[2,3],[1,3],[3],[2,2],[1,2],[2],[1]]
repeatedlyChop heads = heads:repeatedlyChop (chop heads)
----------------------------------------------------------
repeatedlyChop [3]
-- [[3],[2,2],[1,2],[2],[1], [], [], [] ...]
-- this is an infinite list
repeatedlyChop heads = iterate chop heads
repeatedlyChopTillDead heads = takeWhile (not.null) (iterate chop heads)
takeWhileAlive (x:xs) = if null x then [] else x:(takeWhileAlive xs)
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