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@Steell

Steell/readerlens.hs

Last active June 21, 2017 21:56
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MonadReader + Lens
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readerlens.hs
data Foo a = Foo { _unFoo :: a }
makeLenses ''Foo
newtype Newline = Newline { unNewline :: String }
instance Monoid Newline where
mempty = Newline []
mappend (Newline []) b = b
mappend a (Newline []) = a
mappend (Newline a) (Newline b) = Newline $ a `mappend` "\n" `mappend` b
printAll :: ReaderT (Foo (Seq (Foo String))) IO
printAll =
putStrLn =<< unNewline <$> view (unFoo.folded.unFoo.to Newline)
@glguy
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glguy commented Jun 21, 2017 

unlinesOf :: Getting (Endo [String]) s String -> s -> String
unlinesOf l s = unlines (toListOf l s)

printAll :: ReaderT (Foo (Seq (Foo String))) IO ()
printAll = lift . putStr . unlinesOf (unFoo . folded . unFoo) =<< ask

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