I was practicing my Haskell and I came across a weird problem which I was unable to find a solution to on the Internet. I decided to solve this problem: https://www.hackerrank.com/challenges/fibonacci-fp In as many ways I can think of. One way is to perform recursion with memoization where I want to use State monad as a cache. I have GHC 7.10.2 on my Windows 10 and GHC 7.6.2 on my Ubuntu 1
我正在练习我的Haskell，遇到了一个奇怪的问题，我无法在Internet上找到解决方案。 我决定解决这个问题： https://www.hackerrank.com/challenges/fibonacci-fp 我能想到的方式有很多种。 一种方法是在memoization中执行递归，我希望使用State monad作为缓存。 我在我的Windows 10上安装了GHC 7.10.2，在我的Ubuntu 14.04上安装了GHC 7.6.2。 下面的代码在7.6.2上编译（并且运行得很好），并且不会在7.10.2上编译，在我
I have seen all the other memoization tricks and techniques in Haskell but what I am looking for is a straightforward implementation in the level of compiler/interpreter that takes care of memoization for me. For example, consider the following code for the Fibonacci function: fib 0 = 1 fib 1 = 1 fib n = fib (n-1) + fib (n-2) I want some kind of compiler option for ghc (or any other Haskell c
我已经看到了Haskell中所有其他的记忆技巧和技巧，但是我正在寻找的是编译器/解释器级别的简单实现，它为我处理记忆。 例如，考虑斐波那契函数的以下代码： fib 0 = 1 fib 1 = 1 fib n = fib (n-1) + fib (n-2) 我想为ghc（或任何其他Haskell编译器）提供某种编译器选项，默认情况下使用memoization来执行上面的代码。 例如，要计算“fib 10”，首先需要计算“fib 8”和“fib 9”。 而且，计算“fib 9”取决于第一次计算“fib 8”。
By what mechanism is this fibonacci-function memoized? fib = (map fib' [0..] !!) where fib' 1 = 1 fib' 2 = 1 fib' n = fib (n-2) + fib (n-1) And on a related note, why is this version not? fib n = (map fib' [0..] !! n)
这种斐波纳契函数是通过什么机制记忆的？ fib = (map fib' [0..] !!) where fib' 1 = 1 fib' 2 = 1 fib' n = fib (n-2) + fib (n-1) 并在相关说明，为什么这个版本不是？ fib n = (map fib' [0..] !! n)
I was reading the paper authored by Simon Peyton Jones, et al. named “Playing by the Rules: Rewriting as a practical optimization technique in GHC”. In the second section, namely “The basic idea” they write: Consider the familiar map function, that applies a function to each element of a list. Written in Haskell, map looks like this: map f [] = [] map f (x:xs) = f x : map f xs Now supp
我正在阅读Simon Peyton Jones等人撰写的论文。 名为“按规则演奏：在GHC中重写为实用优化技术”。 在第二部分，即他们写的“基本思想”中： 考虑熟悉的map函数，它将函数应用于列表的每个元素。 用Haskell编写， map如下所示： map f [] = [] map f (x:xs) = f x : map f xs 现在假设编译器遇到以下map调用： map f (map g xs) 我们知道这个表达等同于 map (f . g) xs （其中“。”是函数组合），并且我们知道后者表达
The following code runs in about 1.5ms on my computer (compiled with GHC 8.0.1 and -02): import Criterion import Data.Bits import Data.Int import Criterion.Main main :: IO () main = defaultMain [bench "mybench" $ nf (mybench 3840) (0 :: Int)] mybench :: Int -> Int -> Double {-# INLINE mybench #-} mybench n = go 0 n where go s i g | i == 0 = s | otherwise =
以下代码在我的计算机上运行约1.5ms（使用GHC 8.0.1和-02编译）： import Criterion import Data.Bits import Data.Int import Criterion.Main main :: IO () main = defaultMain [bench "mybench" $ nf (mybench 3840) (0 :: Int)] mybench :: Int -> Int -> Double {-# INLINE mybench #-} mybench n = go 0 n where go s i g | i == 0 = s | otherwise = let (w,_) = f 1 0
One code work from runghc, but I can not compile same one with ghc command. Why? Below is my minimal code and environment: https://gist.github.com/1588756 Works well: $ runghc cat.hs Can not compile: $ ghc cat.hs -o cat Macbook air, max os x snow leopard The .cs extension shown in your paste is wrong;1 rename the file to cat.hs and it'll work fine. This error message: ld: warnin
一个代码从runghc工作，但我不能用ghc命令编译同一个代码。 为什么？ 以下是我最小的代码和环境：https：//gist.github.com/1588756 效果很好： $ runghc cat.hs 无法编译： $ ghc cat.hs -o cat Macbook air，max os x雪豹 粘贴中显示的.cs扩展名是错误的; 1将该文件重命名为cat.hs ，它会正常工作。 此错误消息： ld: warning: ignoring file cat.cs, file was built for unsupported file format which is not t
I have this piece of code: {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, KindSignatures, GADTs, FlexibleInstances, FlexibleContexts #-} class Monad m => Effect p e r m | p e m -> r where fin :: p e m -> e -> m r data ErrorEff :: * -> (* -> *) -> * where CatchError :: (e -> m a) -> ErrorEff ((e -> m a) -> m a) m instance Monad m => Effect
我有这段代码： {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, KindSignatures, GADTs, FlexibleInstances, FlexibleContexts #-} class Monad m => Effect p e r m | p e m -> r where fin :: p e m -> e -> m r data ErrorEff :: * -> (* -> *) -> * where CatchError :: (e -> m a) -> ErrorEff ((e -> m a) -> m a) m instance Monad m => Effect ErrorEff ((e
I am trying to do the following: -- enum which wraps arround class (Enum a, Bounded a) => CyclicEnum a where next, prev :: a -> a -- for equatable types this is readily implemented instance (Enum a, Bounded a, Eq a) => CyclicEnum a where next x | x == maxBound = minBound | otherwise = succ x prev x | x == minBound = maxBound | otherwise = pred
我正在尝试执行以下操作： -- enum which wraps arround class (Enum a, Bounded a) => CyclicEnum a where next, prev :: a -> a -- for equatable types this is readily implemented instance (Enum a, Bounded a, Eq a) => CyclicEnum a where next x | x == maxBound = minBound | otherwise = succ x prev x | x == minBound = maxBound | otherwise = pred x 但
I'm a complete newbie in Haskell. One thing that always bugs me is the ambiguity in whether Haskell is a managed(term borrowed from MS) language like Java or a compile-to-native code like C? The GHC page says this "GHC compiles Haskell code either directly to native code or using LLVM as a back-end". In the case of "compiled to native code", how can features like garb
我是Haskell的一名完全新手。 有一件事情总是让我感到困惑的是，Haskell是一种托管（从MS借用的术语）语言（如Java）还是像C这样的编译本机代码？ GHC页面说这个“GHC直接将Haskell代码编译为本地代码或使用LLVM作为后端”。 在“编译为本地代码”的情况下，垃圾收集等功能如何能够在没有JVM之类的情况下实现？ /更新/ 非常感谢你的回答。 从概念上讲，请你帮忙指出我对Haskell垃圾收集的下列理解中的哪一个是正确的： G
I wanted to use {-# LANGUAGE OverloadedStrings #-} but I forgot how it's called. This kind of thing isn't hoogle-able, and also it takes some time finding using google*. Is there somewhere a list of GHC extensions named as they are in the LANGUAGE pragma? * My googling search journey: Google Haskell at wikipedia GHC at wikipedia GHC language features Overload string literal
我想用{-# LANGUAGE OverloadedStrings #-}但我忘记了它的调用方式。 这种事情不是好事，也需要一些时间来寻找使用谷歌*。 是否在某处存在一个GHC扩展名列表，因为它们在LANGUAGE附注中？ *我的谷歌搜索之旅： 谷歌 哈斯克尔在维基百科 GHC在维基百科 GHC语言功能 重载字符串文字 OverloadedStrings 标志参考页面的“语言选项”部分有一个比语言功能页面更容易浏览的列表。 一旦你在那里Ctrl-F搜索“超载”，你