Recent questions tagged haskell

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haskell - Understanding this definition of HList

I'm relatively new to Haskell, and I'm trying to understand one of the definitions of HList. data ... besides avoiding boxing of HCons1? See Question&Answers more detail:os...

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

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534 views

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haskell - What is the significance of algebraic datatypes with zero constructors?

This passage, which unfortunately lacks references, about the development of ADTs in Haskell, from A History of Haskell: ... an ADT be useful? See Question&Answers more detail:os...

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

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487 views

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haskell - Prolog implementation of Quine's algorithm for classical propositional logic (in Quine's "Methods of Logic")

I know only one prover that translates the algorithm that Quine gave for classical propositional logic in his book ... reproduced in this page. 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 deduce KnownNat in two existentials with respect to the singletons library

I was experimenting with the singletons library and I found a case that I don't understand. {-# LANGUAGE GADTs, ... .TypeLits.CmpNat a a1)))) See Question&Answers more detail:os...

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

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582 views

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haskell - Why wrapping the Data.Binary.Put monad creates a memory leak?

I'm trying to wrap the Data.Binary.Put monad into another so that later I can ask it questions like "how ... second part to this question 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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552 views

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haskell - How to show utf8 text with snap and heist?

I have used writeBS writeText from Snap and renderTemplate from heist but none of them seems to support unicode. ... is just some messy 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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565 views

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haskell - MacOSX - cabal install: built failed during the building phase. The exception was: ExitFailure 1 - dist/package.conf.inplace: inappropriate type

using cabal; came accross this error. did cabal install and this happened. failed during the building phase. The ... Compilation version: 7.8.4 See Question&Answers more detail:os...

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

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657 views

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haskell - Gtk2hs windows 7 installation

I did: cabal update cabal install gtk2hs-buildtools But stuck here: >cabal install gtk Resolving dependencies... [ ... see th updated answer. See Question&Answers more detail:os...

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

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521 views

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haskell - Why do we use tuples, if we can use a two dimensional list?

Is there a benefit to specifically reserving varied data-type pairings for tuples like such: [(23, "Jordan"), ... code will not work in Haskell See Question&Answers more detail:os...

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

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802 views

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haskell - Issue installing Snap on macOS Sierra

I'm having trouble installing the Haskell framework Snap on macOS Sierra. Whenever I install it, I get the following ... deleting my ~/.ghc file See Question&Answers more detail:os...

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

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645 views

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haskell - M.Map sudden expected type error

Everything was working great up until about a month or so ago... Suddenly I'm getting berkson.github.io/ ... io/blob/source/source/blog.hs#L330 See Question&Answers more detail:os...

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

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731 views

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haskell - How do I get Parsec to let me call `read` :: Int?

I've got the following, which type-checks: p_int = liftA read (many (char ' ') *> many1 digit <* many ... no control over the file format!) See Question&Answers more detail:os...

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

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729 views

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haskell - Why are these family instance declarations conflicting?

I'm getting an error for this code, and I don't understand where the conflict is. {-# LANGUAGE TypeFamilies, ... 8 Failed, modules loaded: none. See Question&Answers more detail:os...

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

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613 views

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haskell - Getting the data constructor name as a string using GHC.Generics

I'd like something like the following: constrName :: Data a=> a -> String constrName = showConstr . toConstr But for ... m using base-4.8.1.0. See Question&Answers more detail:os...

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

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457 views

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haskell - Why wrapping the Data.Binary.Put monad creates a memory leak? (Part 2)

As in my previous question, I'm trying to wrap the Data.Binary.Put monad into another monad so that ... Could someone please help further? See Question&Answers more detail:os...

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

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650 views

1 answer

haskell - Lazy decoding of a list with Data.Binary

I am lazily encoding lists using this code (taken from this SO question): import Data.Binary newtype Stream a = ... how I can make it lazy? See Question&Answers more detail:os...

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

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734 views

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haskell - How does the <<loop>> error "work" in detail?

I'm working on this tool where the user can define-and-include in [config files | content text-files | etc] their ... to loop in Haskell" 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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535 views

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haskell - looking for a function like break that include the last element

Something that should be easy but somehow I don't find how to do it... let's have the following string: " ... -0987-fe40-61f2-42b0f6fc3e1c"]... See Question&Answers more detail:os...

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

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508 views

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haskell - How to get ReaderT to work with another monad transformer?

I would like to embed ReaderT into another monad transformer. How do I do this? The example below uses Scotty but ... (ReaderT Config IO) () See Question&Answers more detail:os...

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

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621 views

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haskell - Type of a double

Learning Haskell, in ghci: Prelude Data.Ratio> :type 0.15 0.15 :: Fractional a => a Prelude Data.Ratio> ... of 0.15 actually different types? See Question&Answers more detail:os...

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

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740 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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794 views

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haskell sum type multiple declaration error

data A=A data B=B data AB=A|B Which makes a sum type AB from A and B. but the last line induces ... making sum types for user-defined types? See Question&Answers more detail:os...

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

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589 views

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haskell - How to build matrix of zeros using hmatrix?

Trying to use hmatrix, to create a zero marix. For some reason, when I try this on command line, it works: ... } Failed, modules loaded: none. See Question&Answers more detail:os...

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

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421 views

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haskell - Get value from IO rather than the computation itself

Being quite new to Haskell, I'm currently trying to improve my skills by writing an interpreter for a simple imperative ... way out of that..? See Question&Answers more detail:os...

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

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667 views

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haskell - Type error when testing a function with a negative number

I am following along with the Learn you a Haskell for great good, I have implemented take': take' :: (Ord i, Num i) => i ... => i -> [a] -> [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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725 views

1 answer

haskell - Cabal install criterion out of memory

I'm running on a container with 768MB ram and 512 MB swap space. I can't increase either of this. cabal ... have to make do without criterion? See Question&Answers more detail:os...

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

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629 views

1 answer

haskell - Take elements on even positions from the list

Problem: using fold, take from the list elements which are on the even positions: GHCi> evenOnly [1..10] ... something wrong with the syntax. See Question&Answers more detail:os...

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

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523 views

1 answer

haskell - What approach to error handling to use with pipes(-core)?

I'm currently writing some pipes-core/attoparsec plumbing for a small project of mine. I want each parser to ... equivalent to the fourth one. See Question&Answers more detail:os...

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

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