Recent questions tagged haskell

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haskell - Is this property of a functor stronger than a monad?

While thinking about how to generalize monads, I came up with the following property of a functor F: inject :: ... ) in one or both directions. 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 should Applicative be a superclass of Monad?

Given: Applicative m, Monad m => mf :: m (a -> b), ma :: m a it seems to be considered ... Answer posted by @duplode quotes an earlier version. 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 reduce duplication in the build-depends fields of a .cabal file?

Here's a .cabal file: Name: myprogram Version: 0.1 -- blah blah blah Cabal-version: >=1.9.2 Executable ... .4 Haskell Platform 2011.4.0.0 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's the absurd function in Data.Void useful for?

The absurd function in Data.Void has the following signature, where Void is the logically uninhabited type exported by ... going to complain... 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 - Monads as adjunctions

I've been reading about monads in category theory. One definition of monads uses a pair of adjoint functors. A ... anyone given it a thought? 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 exhaustive pattern in function noThirds

So, my Problem is, that I have to write a program that filters all 3 * x (3,6,9...) elements ... list and arithmetic functions are not allowed. 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 - Seeing Typeclass definition in ghci for a specific type

Is there a way to see Typeclass definition in ghci for a specific type? For example, Maybe is defined like this: ... to see that in ghci ? 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 - "=~" raise "No instance for (RegexContext Regex [Char] [String])"

OS: MacOSX 10.7.1 GHC and Haskell-platform from brew. GHCi, version 7.0.4: http://www.haskell.org/ghc ... o"] Any suggestion will be appreciate. 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 - Explicit Purely-Functional Data-Structure For Difference Lists

In Haskell, difference lists, in the sense of [a] representation of a list with an efficient concatenation ... those of function composition? 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 - Pattern matching identical values

I just wondered whether it's possible to match against the same values for multiple times with the pattern ... will occur multiple times? See Question&Answers more detail:os...

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

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1.0k views

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haskell - How to reuse a type variable in an inner type declaration

As part of my Haskell learning process, I like to explicitly type out the type declarations for functions. I would ... apply f to it? Thanks. See Question&Answers more detail:os...

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

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823 views

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haskell - Pseudo-quicksort time complexity

I know that quicksort has O(n log n) average time complexity. A pseudo-quicksort (which is only a quicksort ... , even if they are inefficient. 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 - Odd ghc error message, "My brain just exploded"?

When I try to pattern-match a GADT in an proc syntax (with Netwire and Vinyl): sceneRoot = proc inputs - ... it unsound, or just unimplemented? See Question&Answers more detail:os...

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

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746 views

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haskell - Why does OCaml sometimes require eta expansion?

If I have the following OCaml function: let myFun = CCVector.map ((+) 1);; It works fine in Utop, and ... whether it is read-only or mutable. See Question&Answers more detail:os...

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

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682 views

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haskell - Is there a list of GHC extensions that are considered 'safe'?

Occasionally, a piece of code I want to write isn't legal without at least one language extension. This is ... and which are 'unsafe'? See Question&Answers more detail:os...

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

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846 views

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haskell - An example of a Foldable which is not a Functor (or not Traversable)?

A Foldable instance is likely to be some sort of container, and so is likely to be a Functor as well. Indeed, ... Haskell wiki page missed :-) ) 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 - Handling incremental Data Modeling Changes in Functional Programming

Most of the problems I have to solve in my job as a developer have to do with data modeling. For example in a ... I'm not sure I understand how? See Question&Answers more detail:os...

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

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628 views

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haskell - What is predicativity?

I have pretty decent intuition about types Haskell prohibits as "impredicative": namely ones where a forall appears ... the word "predicate"? See Question&Answers more detail:os...

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

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761 views

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haskell - Explanation of “tying the knot”

In reading Haskell-related stuff I sometimes come across the expression tying the knot , I think I ... explanations of this concept? 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 - When is the difference between quotRem and divMod useful?

From the haskell report: The quot, rem, div, and mod class methods satisfy these laws if y is non-zero: ... how the result is truncated matters? See Question&Answers more detail:os...

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

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717 views

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haskell - Is there a monad that doesn't have a corresponding monad transformer (except IO)?

So far, every monad (that can be represented as a data type) that I have encountered had a corresponding ... be constructed using data types.) See Question&Answers more detail:os...

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

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803 views

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haskell - In what sense is the IO Monad pure?

I've had the IO monad described to me as a State monad where the state is "the real world". The ... unless it specifically adresses my question. See Question&Answers more detail:os...

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

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738 views

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haskell - Understanding a recursively defined list (fibs in terms of zipWith)

I'm learning Haskell, and came across the following code: fibs = 0 : 1 : zipWith (+) fibs (tail fibs) which ... : take 50 fibs Any help? Thanks! 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 - Functional lenses

Could someone explain functional lenses to me? It's a surprisingly difficult subject to google for and I haven' ... functionality than in OO. See Question&Answers more detail:os...

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

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677 views

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haskell - forall in Scala

As shown below, in Haskell, it's possible to store in a list values with heterogeneous types with ... Scala, preferably without subtyping? See Question&Answers more detail:os...

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

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740 views

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haskell - Simplest non-trivial monad transformer example for "dummies", IO+Maybe

Could someone give a super simple (few lines) monad transformer example, which is non-trivial (i.e. not using the ... If yes, when, and why? See Question&Answers more detail:os...

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

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972 views

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haskell - How does the ST monad work?

I understand that the ST monad is something like a little brother of IO, which in turn is the state monad with added ... I to explain it to me. See Question&Answers more detail:os...

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

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700 views

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haskell - Why not be dependently typed?

I have seen several sources echo the opinion that "Haskell is gradually becoming a dependently-typed language". The ... s the 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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