# 99 questions/Solutions/4

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< 99 questions | Solutions(Difference between revisions)

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<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 |
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</haskell> |
</haskell> |

## Revision as of 23:08, 12 January 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' xs = snd $ last $ zip xs [1..] -- Just for fun

length

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