deriving Questions
3
Solved
The definition of deriving on stack overflow is:
"In Haskell, a derived instance is an instance declaration that is
generated automatically in conjunction with a data or newtype
declaration. T...
Nahuatl asked 25/6, 2017 at 9:12
1
Solved
Consider two data declarations:
{-# LANGUAGE GADTs #-}
data X = Int `Y` Int deriving Show
data Z where
W :: Int -> Int -> Z deriving Show
main = do
print (1 `Y` 2)
print (3 `W` 4)
Ru...
Geotropism asked 23/6, 2017 at 20:8
1
Solved
I'm trying to implement a recursive datatype using recursion-schemes. I would like to be able to print it.
import Data.Functor.Foldable
data T1F a = Foo deriving Show
type T1 = Fix T1F
data T2 = ...
Hysteric asked 21/3, 2017 at 18:36
1
Solved
I have the following newtype:
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
newtype Wrap m a = Wrap {runWrap :: m a}
deriving (Functor, Applicative, Monad, MonadTrans)
I'm trying to derive Monad...
Tita asked 24/1, 2017 at 8:50
2
Here's what I'm trying but it doesn't compile:
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleInstances #-}
import Data.Text as T
import Data.Int (Int64)
...
Leafstalk asked 4/1, 2017 at 5:33
1
Solved
Using the cassava package, the following compiles:
{-# LANGUAGE DeriveGeneric #-}
import Data.Csv
import GHC.Generics
data Foo = Foo { foo :: Int } deriving (Generic)
instance ToNamedRecord Foo
...
1
Solved
I've written two monads for a domain-specific language I'm developing. The first is Lang, which is supposed to include everything needed to parse the language line by line. I knew I would want read...
Shrovetide asked 26/4, 2016 at 18:17
3
Solved
Algebraic Data Types (ADTs) in Haskell can automatically become instances of some typeclasses (like Show, Eq) by deriving from them.
data Maybe a = Nothing | Just a
deriving (Eq, Ord)
My questi...
Krasnodar asked 5/10, 2010 at 14:29
1
Solved
What's the simplest way to create a custom type that behaves like a number?
I want type-checking that prevents mixing different units in my program, but I still want to be able to easily per...
2
Solved
Documentation of both Either and Maybe indicate that they have instances of Show.
Either is defined as deriving Show, simply :
data Either a b = Left a | Right b
deriving (Eq, Ord, Read, Show, ...
Bowerbird asked 7/1, 2015 at 22:10
2
Solved
Given a differentiable type, we know that its Zipper is a Comonad. In response to this, Dan Burton asked, "If derivation makes a comonad, does that mean that integration makes a monad? Or is that n...
1
Solved
Haskell can derive the instance for MonadState s in T1 below but not in T2 which is however a very similar type. In which way should I modify the code for T2 so that the instance for MonadState s c...
Ninanincompoop asked 5/9, 2014 at 20:25
3
Solved
Given any container type we can form the (element-focused) Zipper and know that this structure is a Comonad. This was recently explored in wonderful detail in another Stack Overflow question for th...
1
Solved
I have a typeclass Cyclic for which I would like to be able to provide generic instances.
class Cyclic g where
gen :: g
rot :: g -> g
ord :: g -> Int
Given a sum type of nullary constru...
Sculpsit asked 3/4, 2014 at 23:39
3
I am playing with a Red-Black tree:
-- Taken from Okasaki 1999
module RedBlackTree where
--node coloring data
--a node is R (red) or B (black)
data Color = R | B
--tree constructor
--a RBT can b...
1
Solved
I need some help to get js_of_ocaml working. There's not much information about it on the net, and the manual is very sparse (no snippets or usage examples, no comment sections).
I have a Card mod...
Bathyscaphe asked 24/7, 2013 at 0:44
1
Solved
I am basically attempting to see if I can emulate an ORM framework within Haskell, so that if a user wants to make a database model, they would do something like this
data Car = Car {
company :: ...
3
The Data.Binary documentation shows writing an instance by hand. Is there a way around this? I saw here there is another library, SerTH, which has a (Template Haskell based) deriving mechanism, but...
Twilley asked 3/1, 2012 at 15:39
1
Solved
Why Template Haskell ignores standalone deriving declaration in quotation?
{-# LANGUAGE TemplateHaskell, StandaloneDeriving #-}
data Test a = Test a
$([d| deriving instance Show a => Show (Test a)...
Jealousy asked 14/1, 2013 at 10:24
2
Solved
I have a datatype
newtype Zq q = Zq (IntType q)
where 'q' will be an instance of the class
class Foo a where
type IntType a
and 'IntType' is just the underlying representation (i.e. Int, Int...
Ajmer asked 9/7, 2012 at 16:20
2
For example, trying to compile the following code
{-# LANGUAGE StandaloneDeriving, KindSignatures, DataKinds, GADTs#-}
data ExprTag = Tag1 | Tag2
data Expr (tag :: ExprTag) where
Con1 :: Int -&...
Noway asked 16/11, 2012 at 20:29
1
Solved
Could anyone, please, explain what can cause this error?
Error: Invalid base class
I've got two classes where one of them is derived from second:
#if !defined(_CGROUND_H)
#define _CGROUND_H
#i...
Collide asked 9/11, 2012 at 12:53
1
I have a GADT which is only ever used with two different parameters, ForwardPossible and ():
-- | Used when a forward definition is possible.
data ForwardPossible = ForwardPossible deriving (Eq, O...
2
Solved
I have created an entity data model and generated a database from it.
One of the entities is called Template.
Created partial classes to extend the functionality of Template works fine.
If I cre...
Steinbok asked 26/3, 2012 at 18:45
1
Solved
Suppose I have a data type like
data D a = D a a a
and a typeclass
class C c ...
instance (C c1, C c2) => C (c1, c2)
Then, I want to be able to write
data D a = D a a a deriving C
and h...
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