From 6588473adf96a3eb7cfac55820ec022d4533fcbf Mon Sep 17 00:00:00 2001 From: Joe Zhao Date: Mon, 24 Aug 2015 15:45:45 -0600 Subject: Foldables --- monad/h1.hs | 3 +++ monad/h2.hs | 5 +++++ monad/h21.hs | 3 +++ monad/h3.hs | 11 +++++++++++ 4 files changed, 22 insertions(+) create mode 100644 monad/h1.hs create mode 100644 monad/h2.hs create mode 100644 monad/h21.hs create mode 100644 monad/h3.hs (limited to 'monad') diff --git a/monad/h1.hs b/monad/h1.hs new file mode 100644 index 0000000..a6cc093 --- /dev/null +++ b/monad/h1.hs @@ -0,0 +1,3 @@ +instance Monad [] where + return a = [a] + (>>=) as f = concatMap f as diff --git a/monad/h2.hs b/monad/h2.hs new file mode 100644 index 0000000..fce9d81 --- /dev/null +++ b/monad/h2.hs @@ -0,0 +1,5 @@ +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 new file mode 100644 index 0000000..c843dcb --- /dev/null +++ b/monad/h21.hs @@ -0,0 +1,3 @@ +(>>=) 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 new file mode 100644 index 0000000..9439331 --- /dev/null +++ b/monad/h3.hs @@ -0,0 +1,11 @@ +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 -- cgit v1.2.3-70-g09d2