non-exhaustive-patterns

Non-exhaustive patterns [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . Given I have the following code: data Note = C | Db | D | Eb | E | F | Gb | G | Ab | A | Bb | B deriving (Show, Eq, Ord, Enum) next :: Note -> Note next B = C next n = succ n previous :: Note -> Note previous C = B previous n = pred n resolveAscendingInterval :: Int -> Note -> Note resolveAscendingInterval 0

Non-exhaustive patterns [closed]

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Given I have the following code: data Note = C | Db | D | Eb | E | F | Gb | G | Ab | A | Bb | B deriving (Show, Eq, Ord, Enum) next :: Note -> Note next B = C next n = succ n previous :: Note -> Note previous C = B previous n = pred n resolveAscendingInterval :: Int -> Note -> Note resolveAscendingInterval 0 note = note resolveAscendingInterval interval note = resolveAscendingInterval (interval -1) (next note) resolveDescendingInterval :: Int -> Note -> Note resolveDescendingInterval 0 note = note resolveDescendingIInterval interval note = resolveDescendingIInterval (interval -1) (previous

Haskell non-exhaustive patterns in function with `otherwise`

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问题 I am using the following function: combinations :: Int -> [a] -> [[a]] combinations k xs = combinations' (length xs) k xs where combinations' n k' l@(y:ys) | k' == 0 = [[]] | k' >= n = [l] | null l = [] | otherwise = Prelude.map (y :) (combinations' (n - 1) (k' - 1) ys) ++ combinations' (n - 1) k' ys It works just fine for just about any example i can come up with, but when i call it from other functions in my larger project, for some cases I get an exception: Exception: projekt.hs:(34,9)-(38

Calculating the length of an array in haskell - non exhaustive patterns error [duplicate]

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问题 This question already has answers here : It works when loaded from file, but not when typed into ghci. Why? (2 answers) Closed 5 years ago . I've searched around on here and on the net in general and I can't find anything that seems to be answering this question. I've only just starting playing around with Haskell for a module at university and I'm having an issue defining a function to calculate the length of an array (the pre-existing length function essentially). In my lecture notes the

Why doesn't this definition cover all pattern cases?

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问题 So I'm trying to triplize an element, i.e. making 2 other copies of the element. So I've written this: triplize :: [a] -> [a] triplize [x] = concatMap (replicate 3) [x] But I've been getting this error: Non-exhaustive patterns in function triplize I'm new to Haskell, so any pointers are appreciated! 回答1: When you write triplize [x] You are saying that the argument must match the pattern [x] . This pattern represents a list with a single value, which will be assigned to the name x . Note that

In Haskell, why non-exhaustive patterns are not compile-time errors?

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This is a follow-up of Why am I getting "Non-exhaustive patterns in function..." when I invoke my Haskell substring function? I understand that using -Wall , GHC can warn against non-exhaustive patterns. I'm wondering what's the reason behind not making it a compile-time error by default given that it's always possible to explicitly define a partial function: f :: [a] -> [b] -> Int f [] _ = error "undefined for empty array" f _ [] = error "undefined for empty array" f (_:xs) (_:ys) = length xs + length ys The question is not GHC-specific. Is it because... nobody wanted to enforce a Haskell

Non-exhaustive patterns in function [duplicate]

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问题 This question already has answers here : Better exception for non-exhaustive patterns in case (2 answers) Closed 3 years ago . I've got a problem with this code, it should count the longest substring of the same letter in a string, but there is an error: *** Exception: test.hs:(15,0)-(21,17): Non-exhaustive patterns in function countLongest' I know that is the wrong types problem, but i dont know where is the error, or how to find or debug it countLongest :: (Eq a) => [a] -> Int countLongest'