rename fold.hs to folding-lists.hs, change to reflect what's going on…

… the site

folding-lists.hs

@@ -0,0 +1,30 @@
+import Data.Foldable (foldr, foldMap, fold)
+import Prelude hiding (sum)
+
+sum :: [Integer] -> Integer
+sum xs = foldr (+) 0 xs
+
+commaList :: [String] -> String
+commaList xs = foldr commaSep "" xs
+  where
+    commaSep x "" = x
+    commaSep x phrase = x ++ ", " ++ phrase
+
+bulletList :: [String] -> String
+bulletList xs = foldMap bulletItem xs
+  where
+    bulletItem x = "  - " ++ x ++ "\n"
+
+smashTogether :: [String] -> String
+smashTogether xs = fold xs
+
+main =
+  do
+    let numbers = enumFromTo 1 5
+    putStrLn (show numbers)
+    putStrLn (show (sum numbers))
+
+    let words = ["One", "Two", "Three", "Four", "Five"]
+    putStrLn (commaList words)
+    putStr (bulletList words)
+    putStrLn (smashTogether words)

outputs/folding-lists.txt

@@ -0,0 +1,9 @@
+[1,2,3,4,5]
+15
+One, Two, Three, Four, Five
+  - One
+  - Two
+  - Three
+  - Four
+  - Five
+OneTwoThreeFourFive

tools/outputs.nix

@@ -29,6 +29,7 @@ in
         (run "dynamic" ../dynamic.hs {})
         (run "enum-ranges" ../enum-ranges.hs {})
         (run "file-handles" ../file-handles.hs {})
+        (run "folding-lists" ../folding-lists.hs {})
         (run "for-loops" ../for-loops.hs {})
         (run "functions" ../functions.hs {})
         (run "hashing" ../hashing.hs {})