/sci/ - Science & Math » Thread #13726101

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Anonymous Thu 07 Oct 19:05:52 2021 No.13726101 View Reply Original Report

Quoted By: >>13726110 >>13726615

what is monad?

Anonymous

Anonymous Thu 07 Oct 2021 19:07:31 No.13726110 Report

Quoted By:

>>13726101
a monoid on a group of endofunctors

Anonymous

Anonymous Thu 07 Oct 2021 21:19:18 No.13726615 Report

Quoted By: >>13726636

>>13726101
A monad is a monoid in the category of endofunctors.

A monad is a kind of container. You can wrap a type in a monad, an pass it through a lifted function. This makes it unbelievably easy to do error handling, or functional parsing, for instance using Parsec.

Anonymous

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Anonymous Thu 07 Oct 2021 21:27:01 No.13726636 Report

Quoted By:

>>13726615

Anonymous

Anonymous Thu 07 Oct 2021 22:43:36 No.13726845 Report

Quoted By: >>13727143

A monad can be though of as the abstraction or pattern for types depending on types.
A function needs a value to become a value;
a monad needs a type to become a type.

Anonymous

Anonymous Fri 08 Oct 2021 00:34:52 No.13727143 Report

Quoted By: >>13728958

>>13726845
>a monad needs a type to become a type
That's true of anything with kind * -> * and doesn't even work because monads have kind (* -> *) -> Constraint

Anonymous

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Anonymous Fri 08 Oct 2021 00:35:58 No.13727148 Report

Quoted By:

Anonymous

Anonymous Fri 08 Oct 2021 14:37:13 No.13728958 Report

Quoted By: >>13729198

>>13727143
>>13727143
You are right, any type of kind *->* works for that.
I was under the impression, that anything of that kind could fit a monad, but maybe you can correct me!
Also what does Constraint mean here?

If we take the List Monad for example we can Just add a type and get the complete List Monad for Integers.

Anonymous

Anonymous Fri 08 Oct 2021 15:50:26 No.13729198 Report

Quoted By:

>>13728958
Constraint is like when you have "Num a => ..." in a type declaration. It ensures that "a" is a type with a Num typeclass.
Since monads have kind "(* -> *) -> Constraint", in the constraint "Monad m => ...", "m" must have kind * -> *

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