haskell

How to write a recursion function in haskell

别来无恙 提交于 2020-04-10 14:27:20
问题 How can I write a function in Haskell which takes a list and a number and it removes all the elements greater than that number and returns the list. remove [5, 4, 3, 9, 1 ] 5 should return [5,4,3,1] I wrote the following method which is becoming infinite loop some where when it hits the greater than the given number. I am getting out [5,4,3 and then program is not ending. remove l1 x = if (null l1 == True) then l1 else if (head l1 > x) then remove (drop 0 l1) x else ((head l1) : remove (tail

Is every Alternative Monad Filterable?

余生颓废 提交于 2020-04-10 08:06:08
问题 The category of sets is both cartesian monoidal and cocartesian monoidal. The types of the canonical isomorphisms witnessing these two monoidal structures are listed below: type x + y = Either x y type x × y = (x, y) data Iso a b = Iso { fwd :: a -> b, bwd :: b -> a } eassoc :: Iso ((x + y) + z) (x + (y + z)) elunit :: Iso (Void + x) x erunit :: Iso (x + Void) x tassoc :: Iso ((x × y) × z) (x × (y × z)) tlunit :: Iso (() × x) x trunit :: Iso (x × ()) x For the purposes of this question I

Is every Alternative Monad Filterable?

谁说胖子不能爱 提交于 2020-04-10 08:06:08
问题 The category of sets is both cartesian monoidal and cocartesian monoidal. The types of the canonical isomorphisms witnessing these two monoidal structures are listed below: type x + y = Either x y type x × y = (x, y) data Iso a b = Iso { fwd :: a -> b, bwd :: b -> a } eassoc :: Iso ((x + y) + z) (x + (y + z)) elunit :: Iso (Void + x) x erunit :: Iso (x + Void) x tassoc :: Iso ((x × y) × z) (x × (y × z)) tlunit :: Iso (() × x) x trunit :: Iso (x × ()) x For the purposes of this question I

Is every Alternative Monad Filterable?

|▌冷眼眸甩不掉的悲伤 提交于 2020-04-10 08:05:27
问题 The category of sets is both cartesian monoidal and cocartesian monoidal. The types of the canonical isomorphisms witnessing these two monoidal structures are listed below: type x + y = Either x y type x × y = (x, y) data Iso a b = Iso { fwd :: a -> b, bwd :: b -> a } eassoc :: Iso ((x + y) + z) (x + (y + z)) elunit :: Iso (Void + x) x erunit :: Iso (x + Void) x tassoc :: Iso ((x × y) × z) (x × (y × z)) tlunit :: Iso (() × x) x trunit :: Iso (x × ()) x For the purposes of this question I

雪崩利器 hystrix-go 源码分析

♀尐吖头ヾ 提交于 2020-04-09 01:52:03
阅读源码的过程,就像是在像武侠小说里阅读武功秘籍一样,分析高手的一招一式,提炼出精髓,来增强自己的内力。 之前的帖子说了一下 微服务的雪崩效应和常见的解决方案 ,太水,没有上代码怎么叫解决方案。 github 上有很多开源的库来解决 雪崩问题 ,比较出名的是 Netflix 的开源库 hystrix 。集 流量控制 、 熔断 、 容错 等于一身的 java 语言的库。今天分析的源码库是 hystrix-go ,他是 hystrix 的的 go 语言版,应该是说简化版本,用很少的代码量实现了主要功能。很推荐朋友们有时间读一读。 使用简单 hystrix 的使用是非常简单的,同步执行,直接调用 Do 方法。 err := hystrix.Do( "my_command", func () error { // talk to other services return nil }, func (err error) error { // do this when services are down return nil }) 异步执行 Go 方法,内部实现是启动了一个 gorouting ,如果想得到自定义方法的数据,需要你传 channel 来处理数据,或者输出。返回的 error 也是一个 channel output := make( chan bool, 1) errors :

What does a quoted string in the import syntax `import “cryptonite” Crypto.Hash` mean?

落爺英雄遲暮 提交于 2020-04-06 04:56:45
问题 As stated in the title. There is a codebase, where I have seen the following syntax import "cryptonite" Crypto.Hash (Context, Digest, SHA256, hash, hashFinalize, hashInit, hashUpdate) This syntax doesn't seem to be mentioned on haskell wiki on imports. What does the "cryptonite" string do here? Where does this syntax come from? Is is part of Haskell2010 and if it is so where in the language report is it mentioned? 回答1: This is extra syntax that is supported when using the PackageImports

What does a quoted string in the import syntax `import “cryptonite” Crypto.Hash` mean?

╄→尐↘猪︶ㄣ 提交于 2020-04-06 04:56:04
问题 As stated in the title. There is a codebase, where I have seen the following syntax import "cryptonite" Crypto.Hash (Context, Digest, SHA256, hash, hashFinalize, hashInit, hashUpdate) This syntax doesn't seem to be mentioned on haskell wiki on imports. What does the "cryptonite" string do here? Where does this syntax come from? Is is part of Haskell2010 and if it is so where in the language report is it mentioned? 回答1: This is extra syntax that is supported when using the PackageImports

Calling Haskell functions from Python

坚强是说给别人听的谎言 提交于 2020-03-30 18:32:09
问题 I want to use some Haskell libraries (e.g. Darcs, Pandoc) from Python, but it seems there’s no direct foreign function interface to Haskell in Python. Is there any way to do that? 回答1: Provided you can get your Python code to call C, you can call Haskell functions that have been exported via the FFI Another approach would be to write a standard IPC interface, in the case of darcs and pandoc just calling them as vanilla executables and parsing their output might be the way to go. As to

Calling Haskell functions from Python

房东的猫 提交于 2020-03-30 18:30:54
问题 I want to use some Haskell libraries (e.g. Darcs, Pandoc) from Python, but it seems there’s no direct foreign function interface to Haskell in Python. Is there any way to do that? 回答1: Provided you can get your Python code to call C, you can call Haskell functions that have been exported via the FFI Another approach would be to write a standard IPC interface, in the case of darcs and pandoc just calling them as vanilla executables and parsing their output might be the way to go. As to

Haskell : using the `find` function on a list of tuples

懵懂的女人 提交于 2020-03-28 07:06:51
问题 I was wondering if anyone could help me. Suppose I have a tuple of type (String,Int) , and a list of such tuples [("Strength",12),("Stamina",60),("Health",100)] . How can I use the function find to extract the Int value of the tuple ("Stamina",60) if I don't actually know what order the tuples are inside the list but only that a certain tuple containing the string "Stamina" exists? I tried value = snd ( find ("Stamina", _ ) stats ) where stats is the list of tuples and value is defined as