# 99 questions/Solutions/4

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< 99 questions | Solutions(Difference between revisions)

Danwizard208 (Talk | contribs) (Added another two solutions) |
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<haskell> |
<haskell> |
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− | myLength' = foldl (\n _ -> n + 1) 0 |
+ | myLength' = foldl (\n _ -> n + 1) 0 |

− | myLength'' = foldr (\_ n -> n + 1) 0 |
+ | myLength'' = foldr (\_ n -> n + 1) 0 |

− | myLength''' = foldr (\_ -> (+1)) 0 |
+ | myLength''' = foldr (\_ -> (+1)) 0 |

− | myLength'''' = foldr ((+) . (const 1)) 0 |
+ | myLength'''' = foldr ((+) . (const 1)) 0 |

+ | myLength''''' = foldr (const (+1)) 0 |
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</haskell> |
</haskell> |
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<haskell> |
<haskell> |
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myLength' xs = snd $ last $ zip xs [1..] -- Just for fun |
myLength' xs = snd $ last $ zip xs [1..] -- Just for fun |
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+ | myLength'' = snd . last . (flip zip [1..]) -- Because point-free is also fun |
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</haskell> |
</haskell> |
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## Revision as of 20:38, 21 November 2011

(*) Find the number of elements of a list.

myLength :: [a] -> Int myLength [] = 0 myLength (_:xs) = 1 + myLength xs

myLength' = foldl (\n _ -> n + 1) 0 myLength'' = foldr (\_ n -> n + 1) 0 myLength''' = foldr (\_ -> (+1)) 0 myLength'''' = foldr ((+) . (const 1)) 0 myLength''''' = foldr (const (+1)) 0

myLength' xs = snd $ last $ zip xs [1..] -- Just for fun myLength'' = snd . last . (flip zip [1..]) -- Because point-free is also fun

myLength = sum . map (\x -> 1)

length

Prelude