Make it possible to evaluate monadic actions when assigning record fields

[Adde]

Monads are a part of Haskell. The more tiresome monads are to use, the
more tiresome Haskell is to use. I suggest we leave the decision of
where and when to use them to each individual user of the language.

/Adde

> In any case, I'm *strongly against* further syntactic sugar for
> monads,
> including #1518. The more tiresome monads are, the more incentive you
> have to avoid them.
> 
> Regards,
> apfelmus