More list-related functions

Author: ZeppLu

lyh07.hs

@@ -1,4 +1,48 @@
 -- LYH Chapter 7. Modules --
 
 
--- NEXT: here
+import Data.List
+import Data.Function (on)
+
+-- More list-related functions
+-- `intersperse', `intercalate', `transpose', `concat'
+join xs xss = concat (intersperse xs xss)
+join' = intercalate
+
+-- `iterate'
+twoPowers = iterate (*2) 1
+
+-- `sort', `group', `groupBy', `nub', `nubBy'
+-- A codewars kata
+uniqueInOrder :: (Ord a, Eq a) => [a] -> [a]
+uniqueInOrder = sort . nub
+uniqueInOrder' :: (Ord a, Eq a) => [a] -> [a]
+uniqueInOrder' = nub . sort
+uniqueInOrder'' :: (Ord a, Eq a) => [a] -> [a]
+uniqueInOrder'' = map head . group . sort
+
+-- `inits', `tails'
+
+-- `find' (-> Maybe a), `findIndex' (-> Maybe a), `findIndices' (-> [a])
+
+-- `isPrefixOf', `isInfixOf', `isSuffixOf'
+
+-- `elemIndex' (-> Maybe a), `elemIndices' (-> [a])
+
+-- `delete', `deleteBy' `(\\)'
+
+-- `union', `unionBy', `intersect', `intersectBy'
+-- `insert'
+
+-- `generic{Length,Take,Drop,SplitAt,Index,Replicate}' and
+--          length,take,drop,splitAt,(!!), replicate
+
+-- `on' from Data.Function
+sameSign :: (Num a, Ord a) => a -> a -> Bool
+sameSign = (==) `on` (compare 0)
+sameSign' :: (Num a, Ord a) => a -> a -> Bool
+sameSign' = (==) `on` signum
+
+-- `sortBy', `insertBy', `maximumBy', `minimumBy'
+
+-- NEXT: Data.Char

rwh03.hs

@@ -59,6 +59,7 @@ nodesAreSame _ _ = False
 
 -- RWH ch03 ex07
 -- Similar to join in python
+-- Actually the same as `intercalate' in Data.List
 intersperse _ []     = []
 intersperse _ [x]    = x
 intersperse j (x:xs) = x ++ j ++ intersperse j xs