polyvariadic

How to create a polyvariadic haskell function?

由 妖精的绣舞 提交于 2019-12-27 11:08:27
问题 I need a function which takes an arbitrary number of arguments (All of the same type), does something with them and afterwards gives a result back. A list of arguments is impracticable in my specific case. As I looked through the haskell libs, I saw that the function printf (from module Text.Printf ) uses a similar trick. Unfortunately, I couldn't understand that magic by looking at the source. Can somebody explain how to achieve this, or at least some webpage/paper/whatever where I could

Help In Declaring Variable Number Of Arguments

由 我的梦境 提交于 2019-12-11 09:27:21
问题 High Guys, I have to define a polymorphic datatype for a tree that can have multiple nodes. Each node can have any number of children and a vlaue. This type will always have at least one node. I am new in Haskell so am asking how can i declare the node to have variable number of arguments. This is what i have now. This is a tree that can have a Node or a node with value (a) and two tree children. Instead of two tree children, i want them to be any number of tree children. (Analoog as java

C++ polymorphism with variadic function parameter

由 馋奶兔 提交于 2019-12-10 10:13:53
问题 I am sharing with you an issue that I got with a class using variadic function parameters. It is the class Thread shown in the following code. It is a wrapper of std::thread in order to use the function pattern. I wanted to use polymorphism with this function in inheriting the class Thread into a new class, Functor, but gcc returns the errors bellow: #include <thread> #include <iostream> using namespace std; template<class... Args> class Thread { public: virtual void operator()(Args...) = 0;

Haskell, polyvariadic function and type inference

由 杀马特。学长 韩版系。学妹 提交于 2019-12-06 08:15:06
While looking for Polyvariadic function examples, I found this resource: StackOverflow: How to create a polyvariadic haskell function? , and there was an answer snippet like this: class SumRes r where sumOf :: Integer -> r instance SumRes Integer where sumOf = id instance (Integral a, SumRes r) => SumRes (a -> r) where sumOf x = sumOf . (x +) . toInteger Then we could use: *Main> sumOf 1 :: Integer 1 *Main> sumOf 1 4 7 10 :: Integer 22 *Main> sumOf 1 4 7 10 0 0 :: Integer 22 *Main> sumOf 1 4 7 10 2 5 8 22 :: Integer 59 I tried out to change it a little bit, just for curiosity, because I found

C++ polymorphism with variadic function parameter

由 天大地大妈咪最大 提交于 2019-12-06 01:26:47
I am sharing with you an issue that I got with a class using variadic function parameters. It is the class Thread shown in the following code. It is a wrapper of std::thread in order to use the function pattern. I wanted to use polymorphism with this function in inheriting the class Thread into a new class, Functor, but gcc returns the errors bellow: #include <thread> #include <iostream> using namespace std; template<class... Args> class Thread { public: virtual void operator()(Args...) = 0; void run(Args... args) { std::thread t(std::forward< Thread<Args...> >(*this), std::forward<Args>(args)

Haskell “Apply”? [duplicate]

由 十年热恋 提交于 2019-12-04 16:45:25
问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Why is such a function definition not allowed in haskell? I'm a newcomer to the world of Haskell, migrating over from Lisp. I'm trying to adjust to Haskell's fundamentally different worldview, and one of the many things that I find new and exciting is the type system. Being a Lisper, I thought I would try to implement in Haskell a function which is very important in the Lisp world: apply . For those who don't

Haskell “Apply”? [duplicate]

由 大城市里の小女人 提交于 2019-12-03 09:52:57
Possible Duplicate: Why is such a function definition not allowed in haskell? I'm a newcomer to the world of Haskell, migrating over from Lisp. I'm trying to adjust to Haskell's fundamentally different worldview, and one of the many things that I find new and exciting is the type system. Being a Lisper, I thought I would try to implement in Haskell a function which is very important in the Lisp world: apply . For those who don't know, apply takes a function and a list of arguments, and invokes the function on those arguments. In Scheme, (apply + '(1 2 3)) is the same as invoking (+ 1 2 3) ,

Polyvariadic Functions in Haskell

由 ╄→гoц情女王★ 提交于 2019-12-03 05:08:36
问题 After reading this article on writing polyvariadic functions in Haskell, I tried to write some of my own. At first I thought I'd try to generalize it - so I could have a function that returned variadic functions by collapsing arguments as given. {-# OPTIONS -fglasgow-exts #-} module Collapse where class Collapse a r | r -> a where collapse :: (a -> a -> a) -> a -> r instance Collapse a a where collapse _ = id instance (Collapse a r) => Collapse a (a -> r) where collapse f a a' = collapse f (f

Polyvariadic Functions in Haskell

由 淺唱寂寞╮ 提交于 2019-12-02 19:28:15
After reading this article on writing polyvariadic functions in Haskell , I tried to write some of my own. At first I thought I'd try to generalize it - so I could have a function that returned variadic functions by collapsing arguments as given. {-# OPTIONS -fglasgow-exts #-} module Collapse where class Collapse a r | r -> a where collapse :: (a -> a -> a) -> a -> r instance Collapse a a where collapse _ = id instance (Collapse a r) => Collapse a (a -> r) where collapse f a a' = collapse f (f a a') However, the compiler didn't like that: Collapse.hs:5:9: Functional dependencies conflict

Haskell, polyvariadic function and type inference

由 有些话、适合烂在心里 提交于 2019-11-30 10:49:19
While looking for Polyvariadic function examples, I found this resource: StackOverflow: How to create a polyvariadic haskell function? , and there was an answer snippet like this: class SumRes r where sumOf :: Integer -> r instance SumRes Integer where sumOf = id instance (Integral a, SumRes r) => SumRes (a -> r) where sumOf x = sumOf . (x +) . toInteger Then we could use: *Main> sumOf 1 :: Integer 1 *Main> sumOf 1 4 7 10 :: Integer 22 *Main> sumOf 1 4 7 10 0 0 :: Integer 22 *Main> sumOf 1 4 7 10 2 5 8 22 :: Integer 59 I tried out to change it a little bit, just for curiosity, because I found
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