# 99 questions/Solutions/4

### From HaskellWiki

< 99 questions | Solutions(Difference between revisions)

Line 8: | Line 8: | ||

<haskell> | <haskell> | ||

− | myLength' | + | 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 | ||

</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

Prelude