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Today's Topics:
1. Re: Applicative on Tree (mike h)
----------------------------------------------------------------------
Message: 1
Date: Tue, 8 Sep 2015 13:47:36 +0000 (UTC)
From: mike h <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Applicative on Tree
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="utf-8"
Thanks I'll work through it.
On Tuesday, 8 September 2015, 0:39, Imants Cekusins <[email protected]>
wrote:
> data Tree a = Node a [Tree a]
well here is something that builds and runs. Not sure if the monad laws apply.
watch out for indents!
{-# LANGUAGE InstanceSigs #-}
module TreeApp where
import Debug.Trace
import Data.Char
data Tree a = Node a [Tree a]? deriving (Show)
instance Functor Tree where
? fmap::(a -> b) -> Tree a -> Tree b
? fmap f (Node x l0) = Node (f x) (fmap f <$> l0)
instance Applicative Tree where
? pure::a -> Tree a
? pure a =? Node a []
? (<*>)::Tree (a -> b) -> Tree a -> Tree b
? (<*>) (Node f _) tra = f <$> tra
instance Monad Tree where
? return::a -> Tree a
? return a = pure a
? (>>=)::Tree a -> (a -> Tree b) -> Tree b
? (>>=) (Node x []) amb = amb x
? (>>=) (Node x l0) amb = Node b (m1 <$> l0)
? ? ? ? where (Node b _) = amb x
? ? ? ? ? ? ? m1 ta = ta >>= amb
f::Char->Int
f = digitToInt
mb::Char->Tree Int
mb c = f <$> (pure c)
main::Char -> Char -> IO ()
main a b = print $ tc4 >>= mb
{-
? do
? ? ? print ti2
? ? ? print ta3
? ? ? tm4 <- tc4
-}
? where tc1 = pure a
? ? ? ? ti2 = f <$> tc1
? ? ? ? ta3 = (Node f []) <*> tc1
? ? ? ? tc4 = Node b [tc1]
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