typeclass

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Haskell type classes and type families (cont'd)

I need some help in figuring a compiler error which is really driving me nuts... I have the following type class:[详细]

2022-12-26 06:22 分类：问答
"Ambigous type variable" error when defining custom "read" function

While trying to compile the following code, which is enhanced version of read build on readMay from Safe package.[详细]

2022-12-24 05:51 分类：问答
Haskell: 'No instance for' arising from a trivial usage of Regex library

Following the (accepted) answer from this question, I am expecting the following to work: Prelude Text.Regex.Posix Text.Regex.Base.RegexLike Text.Regex.Posix.String> makeRegex \".*\"[详细]

2022-12-23 17:47 分类：问答
Deriving arbitrary functions in Haskell

When working with derived instances in Haskell, is it possible to derive functions for arbitrary types, or are we restricted to particular functions?开发者_如何学GoYou can derive instances of the foll[详细]

2022-12-22 15:59 分类：问答
Manipulating the order of arguments to type constructors

I wrote something like this: instance Functor (Eithe开发者_StackOverflow中文版r e) where fmap _ (Left a) = Left a[详细]

2022-12-21 10:55 分类：问答
Is there a way to implement constraints in Haskell's type classes?

Is there some way (any way) to implement constraints in type classes? As an example of what I\'m talking about, suppose I want to implement a Group as a type class. So a type would be a group if ther[详细]

2022-12-20 12:46 分类：问答
Deriving a type and its dependencies

I\'ve been playing with newtype wrappers for my indexes to avoid 开发者_JAVA技巧bugs, and I have some code like this:[详细]

2022-12-17 05:56 分类：问答
What is the effect of type synonyms on instances of type classes? What does the TypeSynonymInstances pragma in GHC do?

I\'m reading Real World Haskell Pg 151, and I\'ve stared at the following passage for over an hour: Recall that String is a synonym for[详细]

2022-12-17 03:43 分类：问答
No instance for (Floating Int)

I am learning Haskell. I have created function which returns multiplication table up to \'n\' in base \'b\'. Numbers are padded to \'w\' digits. As the last step, I want to compute \'w\' automatically[详细]

2022-12-15 11:57 分类：问答
How to match rigid types in a type class instance?

I thought I would try modeling some numerical integration on vector quantities of different dimensionality, and figured that type classes were the way to go.I needed something to define the difference[详细]

2022-12-14 20:02 分类：问答