Difference between revisions of "Instances of List and Maybe"
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(align List and Maybe examples) |
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− | This pages compares the |
+ | This pages compares the [[Typeclassopedia]] classes of List and Maybe, with examples of use. You can run the examples in GHCi. |
{| class="wikitable" |
{| class="wikitable" |
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Line 56: | Line 56: | ||
> fmap (+1) [2, 3] |
> fmap (+1) [2, 3] |
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[3, 4] |
[3, 4] |
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+ | > fmap (+1) [] |
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+ | [] |
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</haskell> |
</haskell> |
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Line 103: | Line 105: | ||
> [1] <|> empty <|> [2] |
> [1] <|> empty <|> [2] |
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[1,2] |
[1,2] |
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+ | > empty <|> [2] |
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+ | [2] |
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</haskell> |
</haskell> |
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<haskell> |
<haskell> |
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> import Control.Applicative |
> import Control.Applicative |
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− | > (Just 1) <|> (Just 2) |
+ | > (Just 1) <|> empty <|> (Just 2) |
Just 1 |
Just 1 |
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> Nothing <|> (Just 2) |
> Nothing <|> (Just 2) |
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<haskell> |
<haskell> |
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− | > |
+ | > mul x' y' = do x<-x'; y<-y' return (x*y) |
− | > |
+ | > mul (Just 2) (Just 5) |
− | Just |
+ | Just 10 |
</haskell> |
</haskell> |
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|} |
|} |
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> squares5 [1,2,3] |
> squares5 [1,2,3] |
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[1,4] |
[1,4] |
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+ | > squares5 [] |
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+ | [] |
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</haskell> |
</haskell> |
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<haskell> |
<haskell> |
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+ | > import Control.Monad |
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> squares5 x' = do x<-x'; guard (x*x<5); return (x*x) |
> squares5 x' = do x<-x'; guard (x*x<5); return (x*x) |
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> squares5 (Just 2) |
> squares5 (Just 2) |
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{| class="wikitable" |
{| class="wikitable" |
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− | |+ |
+ | |+ Foldable |
|- style="text-align: center" |
|- style="text-align: center" |
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! List |
! List |
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Line 204: | Line 211: | ||
> sequenceA [Just 3, Just 4] |
> sequenceA [Just 3, Just 4] |
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Just [3,4] |
Just [3,4] |
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+ | > sequenceA [Just 3, Nothing] |
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+ | Nothing |
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> sequenceA (Just [3,4]) |
> sequenceA (Just [3,4]) |
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[Just 3,Just 4] |
[Just 3,Just 4] |
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</haskell> |
</haskell> |
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|} |
|} |
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+ | |||
+ | |||
+ | To do : MonadFix |
Latest revision as of 15:53, 21 June 2018
This pages compares the Typeclassopedia classes of List and Maybe, with examples of use. You can run the examples in GHCi.
List | Maybe |
---|---|
> import Data.Semigroup
> [1,2] <> [3,4]
[1,2,3,4]
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> import Data.Semigroup
> (Just [1,2]) <> (Just [3,4])
Just [1,2,3,4]
|
List | Maybe |
---|---|
> mempty :: [Int]
[]
> [1,2] <> mempty
[1,2]
|
> mempty :: Maybe [Int]
Nothing
> (Just [1,2]) <> mempty
Just [1,2]
|
List | Maybe |
---|---|
> fmap (+1) [2, 3]
[3, 4]
> fmap (+1) []
[]
|
> fmap (+1) (Just 2)
Just 3
> fmap (+1) Nothing
Nothing
|
List | Maybe |
---|---|
> [(+1),(+2)] <*> [3,4]
[4,5,5,6]
> [] <*> [3,4]
[]
|
> (Just (+1)) <*> (Just 2)
Just 3
> Nothing <*> (Just 2)
Nothing
|
List | Maybe |
---|---|
> import Control.Applicative
> [1] <|> empty <|> [2]
[1,2]
> empty <|> [2]
[2]
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> import Control.Applicative
> (Just 1) <|> empty <|> (Just 2)
Just 1
> Nothing <|> (Just 2)
Just 2
|
List | Maybe |
---|---|
> mul xs ys = do x<-xs; y<-ys; return (x*y)
> mul [1,2] [3,4,5]
[3,4,5,6,8,10]
|
> mul x' y' = do x<-x'; y<-y' return (x*y)
> mul (Just 2) (Just 5)
Just 10
|
List | Maybe |
---|---|
> import Control.Monad
> squares5 x' = do x<-x'; guard (x*x<5); return (x*x)
> squares5 [1,2,3]
[1,4]
> squares5 []
[]
|
> import Control.Monad
> squares5 x' = do x<-x'; guard (x*x<5); return (x*x)
> squares5 (Just 2)
Just 4
> squares5 (Just 3)
Nothing
> squares5 Nothing
Nothing
|
List | Maybe |
---|---|
> foldr (+) 0 [1,2]
3
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> foldr (+) 1 (Just 2)
3
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List | Maybe |
---|---|
> traverse (\x -> [0..x]) [0..2]
[[0,0,0],[0,0,1],[0,0,2],[0,1,0],[0,1,1],[0,1,2]]
> sequenceA [[1,2],[3,4]]
[[1,3],[1,4],[2,3],[2,4]]
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> traverse (\x -> [x, x*x]) (Just 3)
[Just 3,Just 9]
> sequenceA [Just 3, Just 4]
Just [3,4]
> sequenceA [Just 3, Nothing]
Nothing
> sequenceA (Just [3,4])
[Just 3,Just 4]
|
To do : MonadFix