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Today's Topics:
1. Re: applicative default structure (Ovidiu Deac)
----------------------------------------------------------------------
Message: 1
Date: Fri, 23 Dec 2016 14:48:31 +0200
From: Ovidiu Deac <ovidiud...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] applicative default structure
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<cakvse7tdaz9s6mdyyrkjez3vrer_j43+a4_7s+2zgbqfd_o...@mail.gmail.com>
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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 <toa...@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 <ovidiud...@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 <ima...@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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