[Haskell-cafe] Re: nested maybes
gale at sefer.org
Mon Feb 5 09:38:25 EST 2007
>> Why go to the trouble of creating a new monad?
>> The existing ones are fine.
J. Garrett Morris wrote:
> Mainly to keep the type error messages simpler.
There are two ways to get around that problem:
1. Make your functions polymorphic, using
MonadState, MonadError, etc. Each function
mentions only the capabilities that it needs,
without having the whole monad stack in its type.
2. Use a type alias for the monad stack.
(There are other big advantages of both of these.)
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