Recent questions tagged Haskell

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In my humble opinion the answers to the famous question "What is a monad?", especially the most voted ones, ... as the solution to a problem? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell running out of memory with finite lists

I run out of memory trying to run moderate inputs such as this: variation_models 15 25 also running higher ... in memory usage? replicateM? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Expressing do block using only monadic bind syntax

As far as I know, do blocks in Haskell are just some kind of syntactic sugar for monadic bind operators. ... in monadic expressions like print. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - How to return a pure value from a impure method

I know it must sound trivial but I was wondering how you can unwrap a value from a functor and return it as ... it will wrap it back again. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - How to interpret bind/>>= of the function instance?

I'm trying to improve my understanding of Applicatives and Monads by implementing their function instances in Javascript. ... t make much sense. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - withFile vs. openFile

This program produces the output I expect when given an input file of text delimited by : import System.IO main ... lines `fmap` hGetContents h See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Why does GHC make fix so confounding?

Looking at the GHC source code I can see that the definition for fix is: fix :: (a -> a) -> a ... using the first definition over the second? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Converting IO Int to Int

I've created a combobox from converting a xmlWidget to a comboBox with the function castTocomboBox and now I want to ... I use Glade and gtk2hs. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - How to make a type with restrictions

For example I want to make a type MyType of integer triples. But not just Cartesian product of three Integer, I want the type ... x + y + z = 5. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Non-Trivial Lazy Evaluation

I'm currently digesting the nice presentation Why learn Haskell? by Keegan McAllister. There he uses the ... calculations are thrown away. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - What are Alternative's "some" and "many" useful for?

Alternative, an extension of Applicative, declares empty, <|> and these two functions: One or more: some :: f a ... just what are some and many See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - What does "pure" mean in "pure functional language"?

Haskell has been called a "pure functional language." What does "pure" mean in this context? What consequences does this have for a programmer? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Is there a function to flatten a nested list of elements?

How can I flatten a nested list like this: [1, 2, 3, 4] == flatten [[[1,2],[3]],[[4]]] See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - How does foldr work?

Can anybody explain how does foldr work? Take these examples: Prelude> foldr (-) 54 [10, 11] 53 ... about these executions. Any suggestions? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - foldl Implementation with Runtime Errors

Learn You a Haskell explains foldl1: The foldl1 and foldr1 functions work much like foldl and foldr, only you don ... Lee Duhem's correction. . See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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542 views

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haskell - What is a monad?

Having briefly looked at Haskell recently, what would be a brief, succinct, practical explanation as to what a ... lacking in practical detail. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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832 views

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haskell - Typeclass constraints on data declarations

Apparently it's a bad idea to put a typeclass constraint on a data declaration [src], [src]. I haven't personally ... to allow". Why is that? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Foldr/Foldl for free when Tree is implementing Foldable foldMap?

I am a beginner at Haskell and learning from "Learn You a Haskell". There's something I don't understand about ... and foldl for free now... See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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665 views

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haskell - How to correctly curry a function in JavaScript?

I wrote a simple curry function in JavaScript which works correctly for most cases: const add = curry((a, b, c) => ... : true }); } </script> See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - How do I write, "if typeclass a, then a is also an instance of b by this definition."

I have a typeclass MyClass, and there is a function in it which produces a String. I want to use this to imply ... main = do print Foo print Bar See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Integral operators quot vs. div

Type class Integral has two operations quot and div, yet in the Haskell 2010 Language Report it is not specified ... one, and when the other? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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708 views

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haskell - How to compose `not` with a function of arbitrary arity?

When I have some function of type like f :: (Ord a) => a -> a -> Bool f a b = a > b I should like make function ... t -> t1 -> t2 -> t3 -> Bool See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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663 views

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haskell - What is Levity polymorphism

As the title of the question indicates, I want to know what is Levity polymorphism and what is its ... understand the motivation behind it. See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - What is the difference between Int and Integer?

In Haskell, what is the difference between an Int and an Integer? Where is the answer documented? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - What is the purpose of the reader monad?

The reader monad is so complex and seems to be useless. In an imperative language like Java or C++, there is no ... clear this up a little bit? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Abusing the algebra of algebraic data types - why does this work?

The 'algebraic' expression for algebraic data types looks very suggestive to someone with a background in mathematics ... have any meaning? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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831 views

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haskell - Function definition by special cases in GHCi

From a Haskell tutorial: We can write functions on integers by cases. -- Compute the sum of the integers from 1 to ... 0 0 What am I missing? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - New state of the art in unlimited generation of Hamming sequence

(this is exciting!) I know, the subject matter is well known. The state of the art (in Haskell as well as ... with any given set of primes? See Question&Answers more detail:os...

asked Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

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