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Monoid-instance for Load

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This commit is contained in:
Gregor Kleen 2018-05-17 14:14:00 +02:00
parent 03f9bc4f89
commit ead6aacfc2
1 changed files with 13 additions and 0 deletions
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13
src/Model/Types.hs
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@ -85,6 +85,19 @@ data Load -- = ByTutorial { countsToLoad :: Bool } | ByProportion { load :: Rati
deriving (Show, Read, Eq) deriving (Show, Read, Eq)
derivePersistField "Load" derivePersistField "Load"
instance Semigroup Load where
(Load byTut prop) <> (Load byTut' prop') = Load byTut'' (prop + prop')
where
byTut''
| Nothing <- byTut = byTut'
| Nothing <- byTut' = byTut
| Just a <- byTut
, Just b <- byTut' = Just $ a || b
instance Monoid Load where
mempty = Load Nothing 0
mappend = (<>)
{- Use (is _ByTutorial) instead of this unneeded definition: {- Use (is _ByTutorial) instead of this unneeded definition:
isByTutorial :: Load -> Bool isByTutorial :: Load -> Bool
isByTutorial (ByTutorial {}) = True isByTutorial (ByTutorial {}) = True