Recent questions tagged Haskell

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haskell - Acid-state: MonadState instance for Update

I'm trying acid-state. The documentation states that Update st is an instance of MonadState st. I tried ... or my environment id broken. 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 - Cannot find function similar to liftM2

myLiftM2 :: Monad m => (a -> a1 -> m b) -> m a -> m a1 -> m b myLiftM2 f x y = x >>= ( 1 ... r2)) In liftM2 f return b, but myLiftM2 return m b 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 - Why isn't my IO executed in order?

I got a problem with IO not executing in order, even inside a do construct. In the following code I am just keeping ... xs = filter (/= card) xs 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 - Fun with types! Resolving multiple instance declarations

I'm trying to write some Haskell code in which there are multiple data types, each of which can have ... type system and extensions better. 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 - Cabal error: invalid preprocessing directive #-}

$ cabal install arithmoi-0.4.0.3 results in multiple errors like: Math/NumberTheory/Moduli.hs:489:4: error: invalid ... 7.6.3 Thanks in advance! 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 - Lift to Maybe using a predicate

I'm searching for something like liftPredMaybe :: (a -> Bool) -> a -> Maybe a liftPredMaybe p a | p ... such a function in Haskell already? 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 - Works in ghci but not in the file

when I try something in ghci after loading the file like putStrLn $ showManyP "%d" 10 it works but why this don't work ... f in [x:y] ++ ys 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 can undecidable instances actually hang the compiler?

By the time I first read serious criticism on -XUndecidableInstances, I had already completely accustomed to it ... type class instances? 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 - Parse error on input 'if' when trying to use a condition inside a do block

I have the following code and I already tried multiple ways to write this, but I can't make it work. What I ... sentence, but I get the same. 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 Leksah debugger with programs that use readLn and similar

I recently installed Leksah (0.10.0.4 on Windows 7 64 bit), which seems like an interesting IDE for Haskell ... topics. Am I missing something? 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 was wrong with Control.MonadPlus.Free?

The free MonadPlus defined as data Free f a = Pure a | Free (f (Free f a)) | Plus [Free f a] was ... , in particular, what laws didn't hold? 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 - combining StateT with InputT

It is a follow-up to this question. I'm trying to combine shell from @ErikR's answer in my InputT loop. main :: IO [String ... $ (i, h) -> ... } 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 define function only for old versions in GHC?

I have a code that uses the fromRight function defined circa GHC 8.2. But I need to downgrade to GHC 8.0.2, ... an GHC version than 8.2.1? 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 - Tuple and function composition

Is there a better way to express ((a, b) -> a < b) with function composition? I feel like I' ... experimenting with curry only confused me more. 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 take an array slice with Repa over a range

I am attempting to implement a cumulative sum function using Repa in order to calculate integral images. My ... with a different 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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haskell - Proofs' role in Coq extractions

I'm trying to understand what is the role of proofs in Coq extractions. I have the following example of ... m obviously missing something 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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haskell - Compiling to GHC Core

I would like to create a frontend for a simple language that would produce GHC Core. I would like to then ... GHC. Any pointers would help! 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 - Simulate global variable

I'm working on a project in Haskell and I need a global variable. Currently I'm doing this: funcs :: Map. ... can I simulate a global variable? 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 - Why do Maybe/Optional types use a Just/Some type instead of the actual type?

In Idris, the Maybe type is defined as followed: data Maybe a = Just a | Nothing It's defined similarly in ... data Maybe a = a | Nothing 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 can I use contradictory evidence?

While writing about how to do subtyping in Haskell, it occurred to me that it would be very convenient to be ... cannot be given the type a? 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 - XMonad spawn programs on startup in specified workspace

I am trying to configure my xmonad.hs so that when I start my session I start an array of different ... or is there another workaround? 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 - Why does importing Control.Applicative allow this bad code to type check?

I'm helping a friend learn Haskell and he recently created code like this, which type checks and produces a ... execute in that case? 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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haskell - determining function behavior from the type of the function

New to Haskell so sorry if this is very basic This example is taken from "Real World Haskell" - ghci> :type ... it MUST return type 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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haskell - Unifying c -> a -> b and (a -> b) -> c

What is the type inferred by a Haskell type synthesizer when unifying the types c -> a -> b and (a -> b) -> ... me how can I solve it? 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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haskell - Checking for a particular data constructor

Let's say that I defined my own data-Type like data MyData = A arg| B arg2| C arg3 How would I ... True and isMyDataType Int returns False. 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 - Combining lenses

Using a lens library I can apply a modification function to individual targets, like so: Prelude Control.Lens> (1, 'a', 2) ... ~ (*3) (3,'a',6) 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 `Text' with actual type `[Char]'

This might be a really noobish question, but I can't get past this problem (as I just started learning Haskell). ... just a synonym for [Char]? 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 [temporarily] suppress "defined but not used" warnings?

When I prototype Haskell programs, I always get hundreds of warnings like this (not joking): /Users/bob/SourceCode/ ... not work. Many 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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