Recent questions tagged haskell

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haskell - Can I have an unknown KnownNat?

I wonder if I can have my cake and eat it too regarding KnownNats. Can I write code that uses Nats that ... in "runtime types". Just wondering. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Updating record when referenced by multiple data structures

Suppose I have a record, e.g. Person, and I want to be able to look this person up through multiple data ... the problem I've identified above. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - "Couldn't match expected type with actual type" error when using Codec.BMP

I have a very little experience in Haskell and I want to write a simple ray tracer for practice. Because I ... image and print their values? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Variadic compose function?

I'm trying to write a variadic function composition function. Which is basically the (.) except that the second ... ideas? Is it even possible? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Simple type family example errors about non injective type function

I'm trying to understand type families without much success. Here's a minimal example: {-# LANGUAGE TypeFamilies ... the argument-less unit? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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782 views

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haskell - Is there a language with constrainable types?

Is there a typed programming language where I can constrain types like the following two examples? A Probability is ... with Haskell or Agda. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Can someone explain to me why the app function of ArrowApply makes them as powerful as monads?

So I'll break my question into 4 parts, but first some background: I feel relatively comfortable with ... applicative arrows over monads? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Monad join function

While monads are represented in Haskell using the bind and return functions, they can also have another ... does this actually do? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Using cabal with multiple GHC versions

I got both ghc6 and ghc7 on my desktop. To install new packages (for the specific ghc version), I use ... with installation, updates, etc. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - What is going on with the types in this ghci session?

I'm learning Haskell, and I was playing around in ghci when I came across something very puzzling. First, create ... can I tell the difference?) See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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980 views

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haskell - Accessing a Specific Element in a Tuple

Haskell-newbie reporting in. Question is as follows: In Haskell, we have fst and snd that return the first and ... there is some easy way? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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887 views

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haskell - List partitioning implemented recursively

I am a Haskell beginner and I have been experimenting with recursive functions. I am working on a function: ... other variants with recursion. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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772 views

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haskell - Console interactivity in Netwire?

I am testing with the Netwire haskell library and made it work with a simple time wire: import Control.Wire import ... is good practise or not. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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876 views

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haskell - How to write a monad instance for a pair where both arguments have the same type?

Suppose I have a type Pair: data Pair a = Pair a a What is the right way to write a monad instance for it? ... in the Pair b is a semigroup? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Function to output function name

Is it possible in Haskell to implement a function which returns its own function name? A possible type could be (a -> b) -> String. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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902 views

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haskell - Test if all elements of a Foldable are the same

I built a function that verifies that all elements of a foldable structure are equal. Compared to a similar function on the ... ,[1,1]] -> True See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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643 views

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haskell - How much is applicative really about applying, rather than "combining"?

For an uncertainty-propagating Approximate type, I'd like to have instances for Functor through Monad. This ... restrict myself to those. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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860 views

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haskell - Type error with rank-2 types and function composition

Here are some pragmas and some imports: {-# LANGUAGE ScopedTypeVariables #-} import Control.Monad.ST import Data. ... now. Thanks for helping! See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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762 views

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haskell - How to do automatic differentiation on complex datatypes?

Given a very simple Matrix definition based on Vector: import Numeric.AD import qualified Data.Vector as ... expression: gradientDescent go as0 See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Making numeric functions an instance of Num?

I want to be able to compose numeric functions in haskell using binary operators. So, for example, with ... to some reasonably large number. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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871 views

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haskell - Extending an existing type in OCaml

I've been doing some OCaml programming lately to learn the language and to get more acquainted with functional ... (with typeclasses, perhaps)? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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942 views

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haskell - Implement a function to count frequency of each element in a list

I try to write a program which will count the frequency of each element in a list. In: "aabbcabb" Out: [("a",3),("b", ... ',b'),(==',c')] here.. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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921 views

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haskell - How to use an Alex monadic lexer with Happy?

I'm trying to learn using Alex + Happy to build parser, in particular I'm interested in learning to use ... version of this same lexer+parser. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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820 views

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haskell - Restricting a monad to a type class

In Haskell, is there a way to restrict a monad M a so that a satisfy a type class constraint? I am ... constraint such as Ord a? Thanks. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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858 views

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haskell - Two-dimensional zipper

Inspired by the recent question about 2d grids in Haskell, I'm wondering if it would be possible to create ... we still get efficient movement? See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1.4k views

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haskell - Couldn't Match Expected Type Against Inferred Type, Rigid Type Variable Error

What is wrong with this function ? test :: Show s => s test = "asdasd" String is an instance of the Show class ... of `test': test = "asdasd" See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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828 views

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haskell - How can non-determinism be modeled with a List monad?

Can anyone explain (better with an example in plain English) what a list monad can do to model non-deterministic ... a list monad can offer. See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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haskell - Could not find module `Data.Map' -- It is a member of the hidden package

First, I created a new workspace: stack new xxxx stack init stack build then cd xxxapp stack ghci import Data.Map I ... [email protected]'.` See Question&Answers more detail:os...

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

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