haskell

问题 Closed . This question needs to be more focused. It is not currently accepting answers. Closed 6 years ago . Locked . This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions. I've searched on the Internet for comparisons between F# and Haskell but haven't found anything really definitive. What are the primary differences and why would I want to choose one over the other? 回答1: Haskell

问题 I have some classes and their instances. The example shows some nonsensical classes. Their exact nature is not important. {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE TypeSynonymInstances #-} {-# LANGUAGE FlexibleInstances #-} class Foo a where foo :: a -> Int class Bar a where bar :: a -> String instance Foo Int where foo x = x instance Foo String where foo x = length x instance Bar Int where bar x = show x instance Bar String where bar x = x OK, now I

问题 Applicative Programming with Effects, the paper from McBride and Paterson, presents the interchange law : u <*> pure x = pure (\f -> f x) <*> u In order to try to understand it, I attempted the following example - to represent the left-hand side. ghci> Just (+10) <*> pure 5 Just 15 How could I write this example using the right-hand side? Also, if u is an f (a -> b) where f is an Applicative , then what's the function on the right-hand side: pure (\f -> f x) ... ? 回答1: It would be written as

问题 Applicative Programming with Effects, the paper from McBride and Paterson, presents the interchange law : u <*> pure x = pure (\f -> f x) <*> u In order to try to understand it, I attempted the following example - to represent the left-hand side. ghci> Just (+10) <*> pure 5 Just 15 How could I write this example using the right-hand side? Also, if u is an f (a -> b) where f is an Applicative , then what's the function on the right-hand side: pure (\f -> f x) ... ? 回答1: It would be written as

问题 Applicative Programming with Effects, the paper from McBride and Paterson, presents the interchange law : u <*> pure x = pure (\f -> f x) <*> u In order to try to understand it, I attempted the following example - to represent the left-hand side. ghci> Just (+10) <*> pure 5 Just 15 How could I write this example using the right-hand side? Also, if u is an f (a -> b) where f is an Applicative , then what's the function on the right-hand side: pure (\f -> f x) ... ? 回答1: It would be written as

问题 Applicative Programming with Effects, the paper from McBride and Paterson, presents the interchange law : u <*> pure x = pure (\f -> f x) <*> u In order to try to understand it, I attempted the following example - to represent the left-hand side. ghci> Just (+10) <*> pure 5 Just 15 How could I write this example using the right-hand side? Also, if u is an f (a -> b) where f is an Applicative , then what's the function on the right-hand side: pure (\f -> f x) ... ? 回答1: It would be written as

问题 This is a followup to a recent question that wasn't asked clearly. The poster Aditi Jain's clarifications invalidate the answer somewhat that's already posted there, hence this new post. The objective is to check whether there's no diagonally adjacent pair of elements in the nested lists which are negative of one another. The poster is new to Haskell programming. The function signature is: checkNegation :: [[Int]] -> Bool Examples: checkNegation [[1,2], [-2,3]] will return False : [ [ 1 , 2],

问题 This is a followup to a recent question that wasn't asked clearly. The poster Aditi Jain's clarifications invalidate the answer somewhat that's already posted there, hence this new post. The objective is to check whether there's no diagonally adjacent pair of elements in the nested lists which are negative of one another. The poster is new to Haskell programming. The function signature is: checkNegation :: [[Int]] -> Bool Examples: checkNegation [[1,2], [-2,3]] will return False : [ [ 1 , 2],

问题 This is a followup to a recent question that wasn't asked clearly. The poster Aditi Jain's clarifications invalidate the answer somewhat that's already posted there, hence this new post. The objective is to check whether there's no diagonally adjacent pair of elements in the nested lists which are negative of one another. The poster is new to Haskell programming. The function signature is: checkNegation :: [[Int]] -> Bool Examples: checkNegation [[1,2], [-2,3]] will return False : [ [ 1 , 2],

问题 In Scala, I can define an Algebraic Data Type: scala> sealed trait Maybe[A] defined trait Maybe scala> case class Just[A](x: A) extends Maybe[A] defined class Just scala> case object NothingHere extends Maybe[Nothing] defined object NothingHere It's possible to return a function, f , with a return type of Maybe[A] . scala> def f[A](x: A): Maybe[A] = Just(x) f: [A](x: A)Maybe[A] However, it's also possible to specify that a Just[A] is returned. scala> def f[A](x: A): Just[A] = Just(x) f: [A](x