[Haskell-cafe] Downsides of the Prompt Monad

Ertugrul Söylemez esz at posteo.de
Fri Apr 7 12:41:35 UTC 2017


>> For another the same can be achieved with free monads in a more
>> transparent and flexible manner:
>>
>>     import Control.Monad.Free.Class
>>
>>     data PromptF a b x = PromptF (b -> x) a
>>         deriving (Functor)
>
> More accurately,
>
>     data PromptF' p x = forall a. PromptF (a -> x) (p a)
>
> (with the obvious Functor instance).

Are we talking about the same PromptT here?  I was assuming this one:
<https://hackage.haskell.org/package/prompt-0.1.1.2/docs/Control-Monad-Prompt.html#t:PromptT>.

Even if not, it seems to me that it should be an abstraction layer above
free monads.  It could be a very thin layer around F/FT.  That would
facilitate reuse.


Greets
ertes
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