FoldablesHEADmaster

7 files changed, 34 insertions, 0 deletions

diff --git a/foldables/h1.hs b/foldables/h1.hs
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+++ b/foldables/h1.hs
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+-- What is the type of foldMap . foldMap? Or foldMap . foldMap . foldMap, etc.? What do they do? 
+
+foldMap :: Monoid m => (a -> m) -> t a -> m
+
+foldMap . foldMap :: (Foldable t, Foldable t1, Monoid m) => (a -> m) -> t (t1 a) -> m
+-- They fold for multi-level of foldables
diff --git a/monad/h1.hs b/monad/h1.hs
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+++ b/monad/h1.hs
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+instance Monad [] where
+    return a = [a]
+    (>>=) as f = concatMap f as
diff --git a/monad/h2.hs b/monad/h2.hs
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+++ b/monad/h2.hs
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+instance Monad ((->) e) where
+    return f = \_ -> f
+    (>>=) f1 f2 = \r -> f2 (f1 r) r
+    -- f1 :: m a
+    -- f2 :: a -> m b
diff --git a/monad/h21.hs b/monad/h21.hs
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+++ b/monad/h21.hs
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+(>>=) m f = join $ fmap f m
+join x = x >>= id
+fmap f x = x >>= (return . f)
diff --git a/monad/h3.hs b/monad/h3.hs
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+++ b/monad/h3.hs
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+data Free f a = Var a
+              | Node (f (Free f a))
+
+instance Functor f => Functor (Free f) where
+    fmap g (Var a) = g a
+    fmap g (Node a) = fmap g a
+
+instance Functor f => Monad (Free f) where
+    return a = Var a
+    (Var a) >>= g = g a
+    (Node a) >>= g = fmap g a
diff --git a/monadTrans/h1.hs b/monadTrans/h1.hs
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+++ b/monadTrans/h1.hs
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+-- Kind of t in MonadTrans t
+(* -> *) -> * -> *
diff --git a/monadTrans/h2.hs b/monadTrans/h2.hs
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+++ b/monadTrans/h2.hs
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+-- Implement join :: M (N (M (N a))) -> M (N a), given distrib :: N (M a) -> M (N a) and assuming M and N are instances
+-- of Monad. 
+
+join a = fmap join (join $ fmap distrib a)