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11Functors.hs
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11Functors.hs
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import Control.Applicative
import Data.Monoid
-- We can use the following type to simulate our own list
data List a = Empty | Value a (List a) deriving (Show)
-- Make the list a Functor
instance Functor List where
fmap f Empty = Empty
fmap f (Value val (tail)) = ( Value (f val) (fmap f tail))
head':: List a -> a
head' (Value a (tail)) = a
tail':: List a -> List a
tail' (Value a (tail)) = tail
-- Write a function which appends one list on to another
combineLists:: List a -> List a -> List a
combineLists Empty b = b
combineLists a Empty = a
-- Make our list a Monoid
-- Make our list an Applicative
-- Make sure that the List obeys the laws for Applicative and Monoid
-- Create some lists of numbers of different lengths such as:
twoValueList = Value 10 $ Value 20 Empty
-- Use <$> on the lists with a single-parameter function, such as:
plusTwo = (+2)
-- Use <$> and <*> on the lists with a binary function
-- Create some lists of binary functions
-- Use <*> on the binary functions list and the number lists