[Haskell-beginners] understanding function signature alignement

[simkestuff at gmail.com]

Yes, thinking it the terms that something which is absolutely free to be
whatever, can be restricted and reduced into something else while other way
around is not possible is usefull;
thanks

On Fri, Aug 10, 2018 at 12:06 PM Theodore Lief Gannon <tanuki at gmail.com>
wrote:

> You're right that the return type is more restricted than the argument,
> but it's in an *absolute* sense, not a relative one. It's not possible to
> relax `m d` to make it the same type as `c`, but it IS possible to
> constrain `c` to be the same as `m d`! And that's how `id` works here: the
> input in this case is known to be the same type as the output. You need
> something wrapped in a monad, and you already have that, so you just use it
> as-is.
>
> On Thu, Aug 9, 2018, 7:22 AM simkestuff at gmail.com <simkestuff at gmail.com>
> wrote:
>
>> Thanks, it is still a bit fuzzy to me ...
>>
>>
>> I understand what you did  but what confuses me is that when i look at
>> function with signature like
>>
>> f :: Monad m => c -> m d
>>
>> I always think that return type is somehow restricted in comparison to
>> input because it demands that output type is wraped inside something (monad
>> in this case).
>>
>> For such signature to fit id signature (a -> a) ,  c type shoud be also
>> wraped inside monad but it is not case here...
>>
>> Anyhow, I still have to figure it out
>>
>> thanks
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