simpler append function

src/GoodList.hs

@@ -55,9 +55,7 @@ snoc (Multiple a b c) = Multiple a (b `snoc` c)
 append :: GoodList a -> GoodList a -> GoodList a
 append  Empty            ys              = ys
 append (Singleton x)     ys              = cons x ys
-append  xs               Empty           = xs
-append (Multiple a b c) (Singleton y)    = Multiple a (snoc b c) y
-append (Multiple a b c) (Multiple d e f) = Multiple a (snoc b c `append` cons d e) f
+append (Multiple a b c)  ys              = cons a . append b $ cons c ys
 
 join :: GoodList (GoodList a) -> GoodList a
 join Empty = Empty

test/Main.hs

@@ -3,6 +3,10 @@ import GoodList
 
 abc :: GoodList Char
 abc = cons 'a' $ cons 'b' $ cons 'c' Empty
+def :: GoodList Char
+def = cons 'd' $ cons 'e' $ cons 'f' Empty
 
 main :: IO ()
-main = print abc
+main = print abc >>
+       print def >>
+       print (abc `append` def)