Difference between revisions of "99 questions/Solutions/4"
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m (Fix formating) |
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myLength [] = 0 |
myLength [] = 0 |
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myLength (_:xs) = 1 + myLength xs |
myLength (_:xs) = 1 + myLength xs |
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+ | |||
+ | myLength' :: [a] -> Int |
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+ | myLength' list = myLength_acc list 0 -- same, with accumulator |
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+ | where |
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+ | myLength_acc [] n = n |
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+ | myLength_acc (_:xs) n = myLength_acc xs (n + 1) |
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</haskell> |
</haskell> |
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<haskell> |
<haskell> |
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− | myLength' = |
+ | myLength' = foldl (\n _ -> n + 1) 0 |
− | myLength'' = foldr (\ |
+ | myLength'' = foldr (\_ n -> n + 1) 0 |
+ | myLength''' = foldr (\_ -> (+1)) 0 |
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+ | myLength'''' = foldr ((+) . (const 1)) 0 |
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+ | myLength''''' = foldr (const (+1)) 0 |
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+ | myLength'''''' = foldl (const . (+1)) 0 |
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+ | </haskell> |
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+ | |||
+ | <haskell> |
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+ | 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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+ | myLength''' = fst . last . zip [1..] -- same, but easier |
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+ | </haskell> |
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+ | |||
+ | <haskell> |
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+ | myLength = sum . map (\_->1) |
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</haskell> |
</haskell> |
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This is <hask>length</hask> in <hask>Prelude</hask>. |
This is <hask>length</hask> in <hask>Prelude</hask>. |
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+ | |||
+ | -- length returns the length of a finite list as an Int. |
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+ | length :: [a] -> Int |
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+ | length [] = 0 |
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+ | length (_:l) = 1 + length l |
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+ | |||
+ | The prelude for haskell 2010 can be found [http://www.haskell.org/onlinereport/haskell2010/haskellch9.html#x16-1710009 here.] |
Revision as of 19:22, 30 November 2012
(*) Find the number of elements of a list.
myLength :: [a] -> Int
myLength [] = 0
myLength (_:xs) = 1 + myLength xs
myLength' :: [a] -> Int
myLength' list = myLength_acc list 0 -- same, with accumulator
where
myLength_acc [] n = n
myLength_acc (_:xs) n = myLength_acc xs (n + 1)
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'''''' = foldl (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''' = fst . last . zip [1..] -- same, but easier
myLength = sum . map (\_->1)
This is length
in Prelude
.
-- length returns the length of a finite list as an Int. length :: [a] -> Int length [] = 0 length (_:l) = 1 + length l
The prelude for haskell 2010 can be found here.