First: The term monad is a bit vacuous if you are not a mathematician. An alternative term is computation builder which is a bit more descriptive of what they are actually useful for. They are a pattern for chaining operations. It looks a bit like method chaining in object-oriented languages, but the mechanism is slightly … Read more
The $ operator is for avoiding parentheses. Anything appearing after it will take precedence over anything that comes before. For example, let’s say you’ve got a line that reads: putStrLn (show (1 + 1)) If you want to get rid of those parentheses, any of the following lines would also do the same thing: putStrLn … Read more
What is the monomorphism restriction? The monomorphism restriction as stated by the Haskell wiki is: a counter-intuitive rule in Haskell type inference. If you forget to provide a type signature, sometimes this rule will fill the free type variables with specific types using “type defaulting” rules. What this means is that, in some circumstances, if … Read more
The cause for the error you’re getting here is the use of the name count&remove: identifiers in Haskell have to be either alphanumeric (e.g. count_and_remove) or symbolic (e.g. ==, ++, etc.). Identifiers can’t contain both alphanumeric characters and symbols. But that’s just one problem. You also have a reference to y on line 9 that … Read more
There are following approaches. 1) Create a list pf pairs which are all combinations [(10,10),(10,15),..,(15,10),(15,3)..]. Now you can use simple any function on this list to check if any pair add up to given number. getCoupleList :: [a]->[(a,a)] getCoupleList [] = [] getCoupleList [x] = [] getCoupleList (x:xs) = map (\y->(x,y)) xs ++ getCoupleList xs … Read more
Three things that I can see: You have the arguments that you pass to scramble in main the wrong way round. You haven’t defined getContents anywhere. You’re not using getArgs as you require. As you guessed, you only need to get the first argument (as getArgs :: IO [String]); using arg1:_ <- getArgs will indeed … Read more
There’s no such a thing as a for loop in Haskell. To apply a function to each element in a list, you can either use map or a list comprehension. Since you already have a list comprehension (which currently does not do anything), let’s just use that: mainfun xs = [helpfun 2 x | x … Read more
The fundamental algorithm is the same as your vertical shift function, since String is also a list of characters, [Char]. You can generalize your algorithm to a move function since the code for moveVer really only requires a list and has no dependency on Img: move :: Int -> [a] -> [a] move n xs … Read more
I think you may be confusing type variables which are used in type annotations, and the actual values being passed to the function. In your definition of mygcd: mygcd c = a + b Unless a and b are defined elsewhere, this will be an error. In other words, these a, b, and c are … Read more
You can implement it using mapM_/traverse_ or the flipped argument versions: forM_/for_. I prefer for_ since it looks more like the “enhanced for-loop” from languages like Java. import Data.Foldable (for_) myPutStr :: [(Double,String)] -> IO () myPutStr vals = do for_ vals $ \(num, str) -> do putStr str putStr “: ” print (num * … Read more