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Questions tagged [haskell-prelude]

Prelude is the standard Haskell module that is imported by default into all Haskell modules.

Prelude is the standard Haskell module that is imported by default into all Haskell modules unless either there is an explicit import statement for it, or the NoImplicitPrelude extension is enabled.

See full documentation here: http://hackage.haskell.org/package/base-4.10.1.0/docs/Prelude.html

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const function declaration in haskell

I am confused about one particular example of the const function. So the type declaration const :: a -> b->a states that the function accepts two parameters of type a and b and returns a type a. For example: const 5 3 => 5 const 1 2 => 1 This makes…
Julian
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Concisely give priority to non-Prelude functions in ghci

I have the following imports: {-# LANGUAGE DeriveGeneric, OverloadedStrings, DefaultSignatures, TypeOperators, FlexibleContexts, RecordWildCards, FlexibleInstances, ExtendedDefaultRules #-} import qualified Data.Map as Map import qualified…
Mittenchops
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Printing a custom representation of my own datatype in Haskell

Context Important detail, I am using Haskell (NOT CABAL) on repl.it. I would like to print a custom Haskell datatype that I created. I was thinking of an approach similar to Python's __repr__ or __str__ methods, when creating a new class. Something…
NickS1
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Why does my function dropR (reverse of Prelude drop) look the way it does?

I'm still new to programming and to practice writing functions, I attempted to reverse the effects of the Prelude drop; drop :: Int -> [a] -> [a] drop 0 [] = [] drop 0 (x:xs) = x:xs drop n [] = [] drop n (x:xs) = drop (n-1) xs into something I very…
Lumnar
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Im having an error with Haskell with cases that i cant find

So im trying to create this function AgregarMon that basically adds a "Monomio" to "Polinomio" Monomio would end up being an element inside Polinomio which is a list. You are going to understand better in a little bit type Monomio = (Int, Int) type…
Jackal
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Using alternative preludes in haskell

I'm interested in alternative Preludes. I understand there are many choices: https://hackage.haskell.org/packages/#cat:Prelude https://guide.aelve.com/haskell/alternative-preludes-zr69k1hc I understand one simple thing a lot of them fix is text,…
Mittenchops
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Two function in ^ implementation

I don't understand one thing about implementation of ^ in haskell: (^) :: (Num a, Integral b) => a -> b -> a x0 ^ y0 | y0 < 0 = errorWithoutStackTrace "Negative exponent" | y0 == 0 = 1 | otherwise = f x0 y0 where -- f : x0 ^…
talex
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operator comparison and Prelude.compare

Chapter 8 of Programming in Haskell (2e) defines a data Tree and a binary search function occurs: data Tree a = Leaf a | Node (Tree a) a (Tree a) occurs :: Ord a => a -> Tree a -> Bool occurs x (Leaf y) = x == y occurs x (Node l y…
Rahn
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How to exit the "Main" status after Prelude(Haskell) loaded a module?

In Haskell, after using Prelude to load some files Prelude> :l xxxFileName The prompt beomes *Main> xxxx I don't know where the "Main" function come from, as I didn't define any function called "Main". Is this a special status of Haskell's command…
vik santata
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Prelude dhall Error: Connection establishment took too long

Today my dhall project has started crashing on Prelude dependencies, so the main error is: Error: Connection establishment took too long. I use this deps: let List/map = https://prelude.dhall-lang.org/List/map let Map/values =…
javier_orta
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Is there a way to hide gcd?

I am rewriting the gcd function for an assignment, but when I'm trying to hide gcd, like so: import Prelude hiding ((gcd)) I get the error Parse error on input'gcd'. I'm certain I've completed the redefinition of gcd, but I can't stop the…
Alex
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What causes `Prelude.chr: bad argument`?

I have the following Haskell program I wrote, the purpose of which is to function like a Caesar cipher: 1 import System.IO 2 import System.Environment 3 import System.Exit 4 import Data.Char 5 6 shiftRight :: Int -> Char -> Char 7…
sleep furiously
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'show' returns what I want alongside a weird String

I have a function that needs to get all of the Integers in a list and display them as a string, I.E "Beans 1.29" should return 129. My function is as follows multDigitsRecTest :: String -> String multDigitsRecTest [] = "" multDigitsRecTest (x:xs) …
mfergusson
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"Prelude.read: no parse", own data type

I'm trying to read from file two lists of own data type 'BoardEdge'. When I try to run code I get exception: "Main.hs: Prelude.read: no parse" As I suspect I get this on function responsible for validatation of input (validateInput). When I try…
Łukasz Niewiński
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How to create a list of string with the Prelude.functions?

I look for something equivalent to what we can have in Python doing this:: >>> print([func for func in dir(__builtins__) if func[0].islower()]) ['abs', 'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod',…
user3313834
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