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Published on 2010-04-20T13:57:42Z
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I can't figure out what the "| m -> w"-part means in a class definition like this:
class (Monoid w, Monad m) => MonadWriter w m | m -> w
What additional information does this add to the class definition?
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Trying to learn Haskell. I am trying to write a simple function to remove a number from a list without using built-in function (delete...I think). For the sake of simplicity, let's assume that the input parameter is an Integer and the list is an Integer list. Here is the code I have, Please tell me…
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I'm trying to use Haskells Data.Heap module, but I'm incapable of even using it with integers. The only heap I've been capable of using is "empty", which does not take any arguments.
Later on I'll figure out how to instance for my needs, but for now I'd be glad if I was even able to test it with…
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There has been some intermingling of Scala and Haskell communities, and I have noticed now and then people commenting on stuff that's supposed to be easy in Haskell and hard and Scala. Less often (maybe because I read Scala questions, not Haskell ones), I see someone mentioning that something in Scala…
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I have problems installing ghc-mod on my linux machine. cabal worries about "happy" not being available in versione = 1.17:
$ cabal install ghc-mod
Resolving dependencies...
[1 of 1] Compiling Main ( /tmp/haskell-src-exts-1.14.0-1357/haskell-src-exts-1.14.0/Setup.hs, /tmp/haskell-src-exts-1…
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fibs :: [Int]
fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)]
This generates the Fibonacci sequence.
I understand the behaviour of the guards, of :, zip and tail, but I don't understand <-. What is it doing here?
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I already tried this on Reddit, but there's no sign of a response - maybe it's the wrong place, maybe I'm too impatient. Anyway...
In a learning problem I've been messing around with, I realised I needed a typeclass for functions with operations for applying, composing etc. Reasons...
It can be…
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I have a Haskell typeclass question. I can't munge the syntax to get this (seemingly reasonable) program to compile under GHC.
import Control.Concurrent.MVar
blah1 :: [a] -> IO ([a])
blah1 = return
blah2 :: [a] -> IO (MVar [a])
blah2 = newMVar
class Blah b where
blah :: [a] -> IO (b…
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I'm trying to implement the Cantor Pairing Function, as an instance of a
generic Pair typeclass, as so:
module Pair (Pair, CantorPair) where
-- Pair interface
class Pair p where
pi :: a -> a -> p a
k :: p a -> a
l :: p a -> a
-- Wrapper for typing
newtype CantorPair a =…
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How would one encode the following constraint in Scala (pseudocode)?
def foo(x: T forSome { type T has a Numeric[T] instance in scope }) = {
val n= implicitly[...] // obtain the Numeric instance for x
n.negate(x) // and use it with x
}
In words: I need a type class instance for my input argument…
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When profiling a Haskell program written in GHC, the names of typeclass functions are mangled in the .prof file to distinguish one instance's implementations of them from another. How can I demangle these names to find out which type's instance it is?
For example, suppose I have the following program…
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