Hi Carl, --------------------------------------- snip --------------------------------------- module BeginnerStreams where -- 1. First try: -- Contract: Input lists are sorted. -- -- Notes: -- -- (!) Duplicate elements are allowed. -- (!) Sort `Left` before `Right`. sorts :: Ord a => [a] -> [a] -> [Either a a] sorts (l : ls) (r : rs) | l <= r = Left l : sorts ls (r : rs) | otherwise = Right r : sorts (l : ls) rs -- l > r sorts [] (r : rs) = Right r : sorts' Right rs sorts (l : ls) [] = Left l : sorts' Left ls sorts [] [] = [] sorts' e (i : is) = e i : sorts' e is sorts' _ [] = [] -- The difficulty for me was: "Either". -- I forgot about it while defining and -- did wrong in defining the empty list -- cases in my first definition: -- -- sorts ls rs = ls ++ rs -- -- That isn't possible without constructor application, -- because of the output type "[Either a a]". Is it? -- -- Wish there would be GHCi in the exam. -- Where else did I fail and didn't notice it? -- What higher order functions would you use to define "sorts"? -- 2. First try: -- I'm not sure, what do you mean by 'value itself'? -- Why is the second tuple (2,1)? Ah, I see, is it sth. like: -- -- [1,3] is index 0 and becomes (0,1), (03) -- [2,3] 1 (1,2), (1,3) -- ... -- -- And those sorted in ascending order by the sum of the components? -- Is it possible to stream this computation without blocking? -- Is the list-of-lists sorted? --------------------------------------- snip --------------------------------------- The exercises from old exams that I have solved are at: https://github.com/pascal-knodel/Programming-Paradigms-KIT-2014-2015/tree/ma... Pascal