Is join useful for every monad?

[Dannyu NDos]

Welp. So IO (IO a) is a thing.

Will I ever encounter ReadPrec (ReadPrec a)?

2019년 10월 14일 (월) 14:42, Dmitrii Kovanikov <kovanikov at gmail.com>님이 작성:

> Data types like `IO (IO a)` are useful and their usage is described in the
> following blog post:
>
> * http://www.haskellforall.com/2018/02/the-wizard-monoid.html
>
> One function from the example uses `join` directly:
>
> runWizard :: IO (IO a) -> IO a
> runWizard = join
>
> On Mon, Oct 14, 2019 at 7:55 AM Dannyu NDos <ndospark320 at gmail.com> wrote:
>
>> join is surely useful for Maybe and [].
>>
>> But IO (IO a)? ReadPrec (ReadPrec a)? ST s (ST s a)? When the heck could
>> I encounter such types?
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