Recent questions tagged Haskell

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How can I make (a, a) a Functor without resorting to a newtype? Basically I want it to work like this: ... nicely, i.e. without a newtype? 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 multiple states in StateT

I am writing a program that runs as a daemon. To create the daemon, the user supplies a set of ... in advance for any suggestions. 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 - ExitFailure 9 when trying to install ghc-mod using Cabal

When I try to install it with cabal, I get ~$ cabal install ghc-mod Resolving dependencies... [1 of 1] ... 1.13.5 which failed to install. 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 is catching an exception non-pure, but throwing an exception is pure?

In Haskell, you can throw an exception from purely functional code, but you can only catch in IO code ... purely functional languages handle it? 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 - Creating infinite list out of ADT

In Haskell, > a = [1,1..] creates an infinite list. Now I have the following data Subunit = O | P ... be able to create an infinite list? 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 - Stack build fails due to missing package although stack ghci works

I am trying to build a simple program in Haskell using stack. I created a new project using stack new and did ... you very much for your 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 - What's the most standard/generic way to zip a traversable with a list?

Traversable is in a sense the class of containers whose structure has a path (that can correspond to a list), ... figure out what it would be. 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 - In Functional Programming, is it considered a bad practice to have incomplete pattern matchings

Is it generally considered a bad practice to use non-exhaustive pattern machings in functional languages like Haskell or ... well after all ... 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 - Advantages of strict fields in data types

This may now be a bit fuzzy, but I've been wondering that for a while. To my knowledge with !, one can make sure ... t I leave it lazy as it is? 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 - Is there a fast algorithm to determine the godel number of a term of a context free language?

Suppose we have a simple grammar specification. There is a way to enumerate terms of that grammar that guarantees that ... - in that case, 9? 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's so special about 'return' keyword

When I seemed to understand what return is for in Haskell, I tried to play with different alternatives and ... (finallyMyLastStepG y) JustG 9 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 set my GHCi prompt to a lambda character on Windows?

I want to have a lambda (λ) symbol as my prompt in GHCi (7.8) on Windows 7, so I set up my . ... get Windows to recognize the λ symbol properly? 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 - Practical use of curried functions?

There are tons of tutorials on how to curry functions, and as many questions here at stackoverflow. However, ... and no added flexibility... 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 - Yesod: Getting a database entity by ID from an Int

I'm new to both Haskell and Yesod, and am trying to build a simple web application that can answer queries from an ... seem to be stuck... :) 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 does 'qualified' mean in 'import qualified Data.List' statement?

I understand import Data.List. But what does qualified mean in the statement import qualified Data.List? 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 work with AST with Cofree annotation?

I have this simple Expr AST and I can easily convert it to String. import Prelude hiding (Foldable) import ... to solve this annotation problem? 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 - exceptions and monad transformers

I'm using the EitherT monad transformer. Combining it with the IO monad, I'm afraid I would get an exception and it ... it's meant to be done. 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 do the parentheses signify in (x:xs) when pattern matching?

when you split a list using x:xs syntax why is it wrapped in a parentheses? what is the significance of the parentheses? ... x:xs] or just x: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 - efficiently checking that all the elements of a (big) list are the same

Problem Let us suppose that we have a list xs (possibly a very big one), and we want to check that all ... other comment is welcome. Thank you! 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 GHC assembly output

When compiling a haskell source file using the -S option in GHC the assembly code generated is not clear. There' ... parts in the haskell code? 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 - Make GHC only type-check?

Is there a way, either standard, or a clever hack, to make invoking GHC on a file only run the type- ... about the command-line program, 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 - Why MonadPlus and not Monad + Monoid?

I'm trying to understand the motivation behind the MonadPlus. Why is it necessary if there are already the ... MonadPlus and Monad + Monoid? 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 - zipWith analogue in Python?

What is the analogue of Haskell's zipWith function in Python? zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] 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 - Scotty: connection pool as monad reader

There are trillions of monad tutorial including the reader and it seems all clear when you read about it. But when ... access pipe master db 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 - How to design a monadic stack?

How do you design and build your monadic stacks? For the first time I need to build a monadic stack (using ... $ print "Thanks!" 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 - Flipped / reversed fmap (<$>)?

I found defining the following (%) = flip fmap I can write code like this: readFile "/etc/passwd" % lines % ... not to write code like 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 - Data families vs Injective type families

Now that we have injective type families, is there any remaining use case for using data families over type families? ... all under one GADT... 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 express existential types using higher rank (rank-N) type polymorphism?

We're used to having universally quantified types for polymorphic functions. Existentially quantified types are ... universal type quantifiers? See Question&Answers more detail:os...

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

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