[Haskell-beginners] applicative default structure

[Ovidiu Deac]

So normally it should fail but the default typing in ghci is the one who
makes our life easier.

Thanks for the explanation!

On Thu, Dec 22, 2016 at 5:33 PM, David McBride <toad3k at gmail.com> wrote:

> Rather than bailing with an instance error for both Applicative and Num,
> which is the technically the right way, and the way that it used to be in
> the dark ages of ghci.  Instead it chooses types which are probably what
> you wanted.  In this case it defaults f to IO and a to Int, and then runs
> it.
>
> You can read more about type defaulting in ghci here:
> https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghci.html
>
> On Thu, Dec 22, 2016 at 10:18 AM, Ovidiu Deac <ovidiudeac at gmail.com>
> wrote:
>
>> My understanding is that x can take any form required for type-inference.
>> That's fine but what is the "default" structure if you don't specify any?
>>
>> On Thu, Dec 22, 2016 at 5:13 PM, Imants Cekusins <imantc at gmail.com>
>> wrote:
>>
>>> > What is f here?
>>>
>>> anything Applicative:
>>>
>>> Prelude> let a1 = pure 1
>>> Prelude> let a2 = pure 1
>>>
>>> Prelude> (a1::Maybe Int) == a2
>>> True
>>> Prelude> (a1::Maybe Float) == a2
>>> True
>>> Prelude> (a1::Either String Float) == a2
>>> True
>>>
>>>
>>> ​
>>>
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