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## Motivation
Haskell has fine-grained typeclass hierarchies. Consider:
```haskell
class Semigroup a where
() :: a -> a -> a
class Semigroup m => Monoid m where
mempty :: m
-- Def…
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when you import:
```
cats.syntax.foldable._
```
You got two methods which look very similar in terms in what they do:
```
.foldMap[B](f: A => B)(implicit B: Monoid[B]): B
.collectFold[B](…
SimY4 updated
3 years ago
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E.g., right now we have a `Monoid[Int]` defined in the companion object for `Semigroup`.
```scala
scala> import leopards.Semigroup
scala> summon[Semigroup[Int]]
val res0: leopards.Semigroup.gi…
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Reported by **ewaryst** and assigned to **maeder**
Migrated from http://trac.informatik.uni-bremen.de:8080/hets/ticket/692
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Consider the spec
```
logic HasCASL
spec Monoid =
sort Elem
…
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This depends on newtypes; without newtypes, we can't really do this.
As far as I can see, no evidence has been presented that MonoidK and SemigroupK are useful abstractions. So far, all they exist …
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A common use case for the ANY monoid (see #21) is in the ANY_PAIR semiring that is currently in SuiteSparse:GraphBLAS. The PAIR operator is called ONEB in the C spec, and, mathematically, ~FIRST_ONEB~…
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Reducers model append and prepend operations on Monoidal containers.
[Described on slide 9 of this talk by Kmett](http://comonad.com/reader/wp-content/uploads/2009/08/IntroductionToMonoids.pdf)
See …
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In case of failure, one may be interested in only the first few errors, but `Validation` requires that everything be checked regardless. A version with a `Monoid` rather than `Semigroup` constraint co…
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在 haskell 里,function 本身也是 functor, applicative, monad 和 monoid。
## 理念
function 是天然的 container。
```haskell
- b 是 test 函数包含的 value, test a 函数调用是获取 container 内部 value 的方式
test :: a -> b
```
…