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maybe [2014/08/23 20:12] nikolaj |
maybe [2014/09/15 20:17] nikolaj |
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| Line 4: | Line 4: | ||
| data Maybe a = Nothing | Just a | data Maybe a = Nothing | Just a | ||
| deriving (Eq, Ord) | deriving (Eq, Ord) | ||
| - | |||
| - | instance Functor Maybe where | ||
| - | fmap _ Nothing = Nothing | ||
| - | fmap f (Just a) = Just (f a) | ||
| instance Monad Maybe where | instance Monad Maybe where | ||
| + | return x = Just x | ||
| (Just x) >>= k = k x | (Just x) >>= k = k x | ||
| Nothing >>= _ = Nothing | Nothing >>= _ = Nothing | ||
| Line 18: | Line 15: | ||
| return = Just | return = Just | ||
| fail _ = Nothing | fail _ = Nothing | ||
| + | | ||
| + | -- instance Functor Maybe where | ||
| + | -- fmap _ Nothing = Nothing | ||
| + | -- fmap f (Just a) = Just (f a) | ||
| </code> | </code> | ||
| Line 25: | Line 26: | ||
| ==== Parents ==== | ==== Parents ==== | ||
| === Element of === | === Element of === | ||
| - | [[Functor . Haskell]] | + | [[Monad . Haskell]] |
