lab04b: init

lab04/lab.lhs

@@ -0,0 +1,46 @@
+> import Data.List
+
+Experiment with foldl, foldr, and foldl'
+
+First, implement your own version of the foldl function,
+defined as myFoldl
+
+> myFoldl :: (a -> b -> a) -> a -> [b] -> a
+> myFoldl _ _ _ = error "TBD"
+
+
+Next, define a function to reverse a list using foldl.
+
+> myReverse :: [a] -> [a]
+> myReverse _ = error "TBD"
+
+
+Now define your own version of foldr, named myFoldr
+
+> myFoldr :: (a -> b -> b) -> b -> [a] -> b
+> myFoldr _ _ _ = error "TBD"
+
+
+Now try using foldl (the library version, not yours) to sum up the numbers of a large list.
+Why is it so slow?
+
+Instead of foldl, try using foldl'.
+Why is it faster?
+(Read http://www.haskell.org/haskellwiki/Foldr_Foldl_Foldl%27 for some hints)
+
+
+For an extra challenge, try to implement foldl in terms of foldr.
+See http://www.haskell.org/haskellwiki/Foldl_as_foldr for details.
+
+
+Next, using the map function, convert every item in a list to its absolute value
+
+> listAbs :: [Integer] -> [Integer]
+> listAbs _ = error "TBD"
+
+Finally, write a function that takes a list of Integers and returns the sum of
+their absolute values.
+
+> sumAbs :: [Integer] -> Integer
+> sumAbs _ = error "TBD"
+