Recent questions tagged haskell

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haskell - Unit-Testing: Can module re-exports avoid having to "expose" all testable modules

TLDR: Is it possible to use module re-exports to avoid having "expose" all testable modules? I've used ... single source file in cabal? See Question&Answers more detail:os...

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

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847 views

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haskell - What would be the "distinct method" that Traversable has in addition to Foldable?

Foldable is a superclass of Traversable, similarly to how Functor is a superclass of Applicative and Monad. Similar to ... a monad is about. See Question&Answers more detail:os...

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

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889 views

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haskell - How does GHCi pick names for type variables?

When using the interactive GHC interpreter, it's possible to ask for the inferred type of an expression: ... find slightly more readable. 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 - Type signature in a where clause

I've written a function similar to Data.Enumerator.List.map that makes an Iteratee compatible with an Enumerator ... type signature for go. See Question&Answers more detail:os...

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

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866 views

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haskell - Type-threaded heterogenous lists and defaulting(?) with type families?

I'm working on a library where I want to define a recursive class that I've simplified here to: {- ... to my recursive continuation stack? 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 - Flatten a list of lists

I have to write a function that flattens a list of lists. For example flatten [] = [] or flatten [1,2,3,4] ... I can do to fix the type error? 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 - How do I use multiple where clauses in GHCi?

I'm playing around with GHCi for the first time, and I'm having some trouble writing multi-line functions. My ... direction of what I'm missing? 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 I magic up type equality from a functional dependency?

I'm trying to get some sense of MultiParamTypeClasses and FunctionalDependencies, and the following struck me as ... "internally" available? 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 - How to pick a random list element in a pure function?

I want to make a Haskell function that can pick out a random number from a given list. My type signature is: ... -> a What should I 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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850 views

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haskell - IO/Monadic assign operator causing ghci to explode for infinite list

Consider the following program. It runs forever and does nothing useful, but the memory consumption in ghci is ... to the above. 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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944 views

1 answer

haskell regex substitution

Despite the ridiculously large number of regex matching engines for Haskell, the only one I can find that will ... am I stuck with this? 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 - Understanding a rank 2 type alias with a class constraint

I have code that frequently uses functions that look like foo :: (MyMonad m) => MyType a -> MyOtherType a ... get the terseness in both cases? 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 - GHC 7.10 generates slower code than older versions

I realized that the latest version of GHC (7.10.3) produces significantly slower code than an older version. ... should I get myself started? See Question&Answers more detail:os...

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

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959 views

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haskell - How to fix "Illegal datatype context" (use -XDatatypeContexts)?

I am a new learner of Haskell, my code is as follows: data Num a=>Units a = Units a (SymbolicManip a ) ... to fix it? Anyone can help me? 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 - How to flatten IO [[String]]?

I am new to Haskell and have some difficulties wrapping my head around some of it's concepts. While playing ... I solve this problem correctly? See Question&Answers more detail:os...

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

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1.2k views

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haskell - Can't install cairo with cabal on Windows - how to get pkg-config on win?

Configuring cairo-0.12.0... setup.exe: The program pkg-config version >=0.9.0 is required but it could not ... or how to install cairo then ? See Question&Answers more detail:os...

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

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958 views

1 answer

haskell - Checking if one type-level list contains another

Is it possible to write a type-level function that returns True if one type-level list contains another type-level list? ... : a) a ~ '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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1.4k views

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haskell - Why does ParsecT type have 'u' argument?

Documentation for the parsec package states that u argument is used to carry some user state through monadic ... state support to ParsecT? See Question&Answers more detail:os...

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

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852 views

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haskell - Testing QuickCheck properties against multiple types?

I have a type class Atomic, which defines functions for converting certain types to/from a wrapper value (Atom ... supported by the type system? See Question&Answers more detail:os...

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

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716 views

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haskell - Style vs Performance Using Vectors

Here's the code: {-# LANGUAGE FlexibleContexts #-} import Data.Int import qualified Data.Vector.Unboxed as U import ... that can be said 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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1.1k views

1 answer

haskell - Function Composition in R (and high level functions)

Is there something like a function composition in R? I think in haskell it's somthing like "(.)" and in agda ... , are there more? Any pointers? See Question&Answers more detail:os...

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

0 votes

854 views

1 answer

haskell - Testing QuickCheck properties against multiple types?

I have a type class Atomic, which defines functions for converting certain types to/from a wrapper value (Atom ... supported by the type system? See Question&Answers more detail:os...

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

0 votes

741 views

1 answer

haskell - Style vs Performance Using Vectors

Here's the code: {-# LANGUAGE FlexibleContexts #-} import Data.Int import qualified Data.Vector.Unboxed as U import ... that can be said here? See Question&Answers more detail:os...

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

0 votes

896 views

1 answer

haskell - Function Composition in R (and high level functions)

Is there something like a function composition in R? I think in haskell it's somthing like "(.)" and in agda ... , are there more? Any pointers? See Question&Answers more detail:os...

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

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957 views

1 answer

haskell - Why is ListT monad transformer considered buggy - what monad laws it breaks?

I've seen mentioned that ListT is a classic example of a buggy monad transformer that doesn't satisfy the ... is obviously not commutative.) See Question&Answers more detail:os...

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

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838 views

1 answer

haskell - Why are GHC Sparks Fizzling?

I have a simple routine that takes the product of a vector of Double. I am attempting to parallelize this code ... with a spark-based approach. See Question&Answers more detail:os...

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

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945 views

1 answer

haskell - Is there any way to separate infinite and finite lists?

For example, I am writing some function for lists and I want to use length function foo :: [a] -> Bool foo ... Int foo :: FiniteList a -> Bool See Question&Answers more detail:os...

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

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951 views

1 answer

haskell - Why do we need Control.Lens.Reified?

Why do we need Control.Lens.Reified? Is there some reason I can't place a Lens directly into a container? What does reify mean anyway? See Question&Answers more detail:os...

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

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