# 99 questions/Solutions/4

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< 99 questions | Solutions(Difference between revisions)

(correction (foldl) and shortened version of foldr) |
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Line 8: | Line 8: | ||

<haskell> | <haskell> | ||

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

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

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

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

This is <hask>length</hask> in <hask>Prelude</hask>. | This is <hask>length</hask> in <hask>Prelude</hask>. |

## Revision as of 01:39, 20 November 2010

(*) 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

length

Prelude