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Today's Topics:
1. Re: understanding function signature alignement
(simkest...@gmail.com)
2. How to write the FromJSON instance for CUid
(PICCA Frederic-Emmanuel)
3. Re: How to write the FromJSON instance for CUid (David McBride)
4. Re: How to write the FromJSON instance for CUid (David McBride)
5. Re: How to write the FromJSON instance for CUid
(PICCA Frederic-Emmanuel)
6. Re: understanding function signature alignement
(Theodore Lief Gannon)
----------------------------------------------------------------------
Message: 1
Date: Thu, 9 Aug 2018 16:22:17 +0200
From: "simkest...@gmail.com" <simkest...@gmail.com>
To: Hask begginers <beginners@haskell.org>
Subject: Re: [Haskell-beginners] understanding function signature
alignement
Message-ID:
<CAJqT=ykhfzvprb51v1+fmdevu5plypspt6_znax1fqdaplu...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
>
> 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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Message: 2
Date: Thu, 9 Aug 2018 15:37:51 +0000
From: PICCA Frederic-Emmanuel
<frederic-emmanuel.pi...@synchrotron-soleil.fr>
To: "The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell" <beginners@haskell.org>
Subject: [Haskell-beginners] How to write the FromJSON instance for
CUid
Message-ID:
<a2a20ec3b8560d408356cac2fc148e530156b3f...@sun-dag3.synchrotron-soleil.fr>
Content-Type: text/plain; charset="us-ascii"
Hello, I try to write the instance for the CUid[1] type
But I do not know what to do.
instance FromJSON CUid where
parseJSON = ...
{-# INLINE parseJSON #-}
Thansk for your help
[1]
https://hackage.haskell.org/package/base-4.11.1.0/docs/System-Posix-Types.html#t:CUid
------------------------------
Message: 3
Date: Thu, 9 Aug 2018 13:06:40 -0400
From: David McBride <toa...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] How to write the FromJSON instance
for CUid
Message-ID:
<CAN+Tr41yMP4HKkszV_-6NmA-ikn-B5+ssUS=yrogs_ayyud...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You have to worry about json having a floating point number or an integer
that is too large to be represented in a Word32, although you could also
just let it overflow if you don't care too much. There's probably an
easier way to do this, but this is what I came up with.
instance FromJSON CUid where
parseJSON (Number n) = do
case floatingOrInteger n of
Right i | inrange i -> return . CUid . fromIntegral $ i
-- not an integer, or not in range
_ -> mempty
where
inrange :: Integer -> Bool
inrange i = fromIntegral i >= (minBound @Word32) &&
fromIntegral i <= (maxBound @Word32)
-- not a number
parseJSON _ = mempty
On Thu, Aug 9, 2018 at 11:37 AM, PICCA Frederic-Emmanuel <
frederic-emmanuel.pi...@synchrotron-soleil.fr> wrote:
> Hello, I try to write the instance for the CUid[1] type
> But I do not know what to do.
>
> instance FromJSON CUid where
> parseJSON = ...
> {-# INLINE parseJSON #-}
>
> Thansk for your help
>
>
> [1] https://hackage.haskell.org/package/base-4.11.1.0/docs/
> System-Posix-Types.html#t:CUid
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 4
Date: Thu, 9 Aug 2018 13:10:48 -0400
From: David McBride <toa...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] How to write the FromJSON instance
for CUid
Message-ID:
<can+tr43vkz33zgzcb79zngfxh_b-q9_3h5o4eb1rqmxkhf5...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Sorry I really should've tested my code before I hit send.
instance FromJSON CUid where
parseJSON (Number n) = do
case floatingOrInteger n of
Right i | inrange i -> return . CUid . fromIntegral $ i
_ -> mempty
where
inrange :: Integer -> Bool
inrange i = i >= fromIntegral (minBound @Word32) &&
i <= fromIntegral (maxBound @Word32)
parseJSON _ = mempty
On Thu, Aug 9, 2018 at 1:06 PM, David McBride <toa...@gmail.com> wrote:
> You have to worry about json having a floating point number or an integer
> that is too large to be represented in a Word32, although you could also
> just let it overflow if you don't care too much. There's probably an
> easier way to do this, but this is what I came up with.
>
> instance FromJSON CUid where
> parseJSON (Number n) = do
>
> case floatingOrInteger n of
> Right i | inrange i -> return . CUid . fromIntegral $ i
>
> -- not an integer, or not in range
> _ -> mempty
>
> where
> inrange :: Integer -> Bool
> inrange i = fromIntegral i >= (minBound @Word32) &&
> fromIntegral i <= (maxBound @Word32)
>
> -- not a number
> parseJSON _ = mempty
>
>
> On Thu, Aug 9, 2018 at 11:37 AM, PICCA Frederic-Emmanuel <
> frederic-emmanuel.pi...@synchrotron-soleil.fr> wrote:
>
>> Hello, I try to write the instance for the CUid[1] type
>> But I do not know what to do.
>>
>> instance FromJSON CUid where
>> parseJSON = ...
>> {-# INLINE parseJSON #-}
>>
>> Thansk for your help
>>
>>
>> [1] https://hackage.haskell.org/package/base-4.11.1.0/docs/Syste
>> m-Posix-Types.html#t:CUid
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>
>
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Message: 5
Date: Fri, 10 Aug 2018 08:05:21 +0000
From: PICCA Frederic-Emmanuel
<frederic-emmanuel.pi...@synchrotron-soleil.fr>
To: "The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell" <beginners@haskell.org>
Subject: Re: [Haskell-beginners] How to write the FromJSON instance
for CUid
Message-ID:
<a2a20ec3b8560d408356cac2fc148e530156b40...@sun-dag3.synchrotron-soleil.fr>
Content-Type: text/plain; charset="us-ascii"
Hello, and thanks for the reply
What about this
instance FromJSON CGid where
parseJSON x = CGid <$> (parseJSON x :: Parser Word32)
{-# INLINE parseJSON #-}
Do you think that it deal with all the problem you are trying to prevent ?
Cheers
Fred
------------------------------
Message: 6
Date: Fri, 10 Aug 2018 03:05:44 -0700
From: Theodore Lief Gannon <tan...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] understanding function signature
alignement
Message-ID:
<CAJoPsuD2JyuixNpCQh4tWdL1C8GcOk3pYm_P_bUN6D+2W=x...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
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 simkest...@gmail.com <simkest...@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
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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