51,693 questions
0
votes
0
answers
51
views
HLS Server Crashes with VSCode, Linux
I am trying to use VSCode and haskell, I have the following versions of each tool:
cabal: 3.12.1.0
stack: 3.3.1
ghc: 9.4.8
hls: 2.10.0.0
The problem is project ...
- 1
1
vote
3
answers
136
views
In the context of STM, what does a transaction log conceptually look like, and how does it evolve when the transaction succeeds after a few retries?
For instance consider this function, that could be used in a WM to allow moving a window from one desktop to another on a given display,
moveWindowSTM :: Display -> Window -> Desktop -> ...
- 28.9k
3
votes
1
answer
62
views
How do let and case differ in terms of lazyness?
How do let and case differ in terms of lazyness? Where do I find the information myself? And how do I experiment with it in ghci?
Some context
This incomplete piece of code is an excerpt from
Parallel ...
- 28.9k
1
vote
1
answer
67
views
Combination of group and take with Data.List.NonEmpty
I'm refactoring a program by changing [a] to (NonEmpty a) so as to avoid having to checks cases of empty lists, which simplifies a lot of my code. In the old code, at one point I transformed a list as ...
- 1,138
2
votes
1
answer
66
views
How can GHC's fairness guarantee not show up if a thread is descheduled while it is not holding the MVar?
In Parallel and Concurrent Programming in Haskell by Simon Marlow, chapter 7 starts at page 125 with this example,
import Control.Concurrent
import Control.Monad
import System.IO
main :: IO ()
main = ...
- 28.9k
1
vote
2
answers
66
views
Clarification on the importance of the immutability of the state inside an MVar in the context of concurrency
In Parallel and Concurrent Programming in Haskell by Simon Marlow, at pages 133 and 134 the following code is shown:
type Name = String
type PhoneNumber = String
type PhoneBook = Map Name ...
- 28.9k
2
votes
1
answer
99
views
Why should bracket's first argument perform at most one blocking operation?
In Parallel and Concurrent Programming in Haskell by Simon Marlow, the implementation of bracket is shown,
bracket
:: IO a -- ^ computation to run first (\"acquire resource\")...
- 28.9k
3
votes
3
answers
105
views
Does throw behave the same as throwIO, if instantiated as IO a?
I'm reading Parallel and Concurrent Programming in Haskell by Simon Marlow, and I initially read this suggestion fairly lightly,
It is always better to use throwIO rather than throw in the IO monad ...
- 28.9k
-1
votes
0
answers
37
views
How can I get my nix package to build using the method defined in `oneTarget`
I have an example repo demonstrating the problem. From the repo's README.md
Need help making packages
The problem I'm having is making packages the way I would like.
In horizon-platoform-template/...
- 198
4
votes
1
answer
123
views
In Haskell, why toRational (1/0) == infinity is False?
I couldn't find documentation for this behaviour and it looks like a bug ([Edit] it is indeed : gitlab.haskell.org/ghc/ghc/-/issues/10387). Am I missing something ?
In GHCi :
> import GHC.Real
...
- 764
1
vote
1
answer
119
views
Finding bracketings of an expression
I'm trying to find all possible bracketing of an associative operation.
There's only one possibility for n=2 variables: (a + b)
∘
|
+--------+
| |
a b
For n=3, there are 2 ...
- 5,247
4
votes
2
answers
78
views
find and replace with the haskell package Text.RE.TDFA
I'm attempting to replace numbers in a string with twice their value using Haskell's Text.RE.TDFA package. My current approach:
s *=~/ fmap (\x -> show $ 2.0*(read x::Double)) [ed|${doublestring}([...
- 183
2
votes
2
answers
83
views
Illegal functional dependencies using the natural type,
data Zero = Zero
data Succ x = Succ x
class NatToPeano a b | a -> b where
toPean :: b
instance NatToPeano 0 Zero where toPean = Zero
instance (NatToPeano (x-1) a) => NatToPeano x (Succ ...
- 109
3
votes
1
answer
91
views
How to generate HMAC in Haskell Crypton, like with openssl HMAC?
Using Haskell crypton package, I'm trying to generate the same output as openssl dgst but can't figure out what I'm doing wrong. Please help.
openssl dgst:
$ echo "TheMessage" | openssl dgst ...
- 606
3
votes
1
answer
60
views
Unresponsive ghci terminal [duplicate]
I read variables are immutable in haskell and something like the following does not work in haskell.
x = 30
x = x+1
But I still tried this to see what the compiler returns and I got the following :
...
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