haskell

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 1 year ago . Improve this question In many languages there's a function that breaks strings into parts using specified delimiter. It's often called split . You can find it in Python, C#, Java, JavaScript. But Haskell while being quite mature still lacks such function in the standard

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 1 year ago . Improve this question In many languages there's a function that breaks strings into parts using specified delimiter. It's often called split . You can find it in Python, C#, Java, JavaScript. But Haskell while being quite mature still lacks such function in the standard

问题 Hackage has been able to display Markdown READMEs for a while. But as one can see for example on the Hackage page for hpack, Hackage doesn't seem to support the same table syntax as GitHub. Markdown: #### <a name="flags"></a>Flags | Hpack | Cabal | Default | Notes | | --- | --- | --- | --- | | `description` | `description` | | Optional | | `manual` | `manual` | | Required (unlike Cabal) | | `default` | `default` | | Required (unlike Cabal) | Rendered on GitHub: Rendered on Hackage: So, I'm

问题 My goal is to pipe some steps for ghci to run from a bash script and then exit cleanly. The commentary online says to use runhaskell for this. This is the command I'm trying to run: ghci> import System.Random ghci> random (mkStdGen 100) :: (Int, StdGen) With expected result similar to: (-3633736515773289454,693699796 2103410263) When I drop this into a file randomtest.hs and execute it with runhaskell I get the following error:. randomtest.hs:3:1: error: Invalid type signature: random

问题 My goal is to pipe some steps for ghci to run from a bash script and then exit cleanly. The commentary online says to use runhaskell for this. This is the command I'm trying to run: ghci> import System.Random ghci> random (mkStdGen 100) :: (Int, StdGen) With expected result similar to: (-3633736515773289454,693699796 2103410263) When I drop this into a file randomtest.hs and execute it with runhaskell I get the following error:. randomtest.hs:3:1: error: Invalid type signature: random

问题 This really shouldn't be so difficult to find an answer to, but alas I don't... I want to delay the next execution step in a do block. I have found the functions delay , sleep , nanosleep and usleep . And also this question, that doesn't cover how to use any of these, however: Sleep in Haskell. I am getting the same error for all of these, so probably I am doing something wrong fundamentally: Variable not in scope: delay :: Integer -> IO a0 This is my test snippet: main = do { putStrLn "line

问题 This really shouldn't be so difficult to find an answer to, but alas I don't... I want to delay the next execution step in a do block. I have found the functions delay , sleep , nanosleep and usleep . And also this question, that doesn't cover how to use any of these, however: Sleep in Haskell. I am getting the same error for all of these, so probably I am doing something wrong fundamentally: Variable not in scope: delay :: Integer -> IO a0 This is my test snippet: main = do { putStrLn "line

问题 The GHC occurs check prevents you from constructing infinite types. Is its purpose to prevent common errors in code or to prevent the typechecker from looping indefinitely, or both? What cases does it identify and is it possible for a malicious user to trick it (as in a Safe Haskell context) into looping? If the type system is Turing-complete (is it?) I don't understand how GHC can guarantee that the computation will halt. 回答1: Think of type inference as solving a system of equations. Let's

问题 The GHC occurs check prevents you from constructing infinite types. Is its purpose to prevent common errors in code or to prevent the typechecker from looping indefinitely, or both? What cases does it identify and is it possible for a malicious user to trick it (as in a Safe Haskell context) into looping? If the type system is Turing-complete (is it?) I don't understand how GHC can guarantee that the computation will halt. 回答1: Think of type inference as solving a system of equations. Let's

问题 I am trying to prove associativity of type-level lists in such a way that will allow me to convert between equivalent types without carrying around any constraints. Assuming the standard definition of concatenation: type family (++) (xs :: [k]) (ys :: [k]) :: [k] where '[] ++ ys = ys (x ': xs) ++ ys = x ': (xs ++ ys) Suppose, I am given a function: given :: forall k (a :: [k]) (b :: [k]) (c :: [k]). Proxy ((a ++ b) ++ c) given = Proxy -- Proxy is just an example and I would like to call this