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Today's Topics:
1. Re: Grappling with State Monad get (Olumide)
2. Re: Libraries for Playing Audio (Atrudyjane)
3. Re: Grappling with State Monad get (Theodore Lief Gannon)
----------------------------------------------------------------------
Message: 1
Date: Wed, 2 Aug 2017 01:13:12 +0100
From: Olumide <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Grappling with State Monad get
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Of course 's' is not a type variable as its lowercase.
Therefore, get is a monad 'constructed' by the state function, correct?
So, in the do notation the lambda is extracted and used as per the
definition of bind. The context of which we speak therefore must derive
from the next expression(?) in the do notation, which is somewhat
confusing to determine in the example
stackyStack :: State Stack ()
stackyStack = do
stackNow <- get
if stackNow == [1,2,3]
then put [8,3,1]
else put [9,2,1]
Regards,
- Olumide
On 02/08/17 00:35, Theodore Lief Gannon wrote:
> 's' here is not a type variable, it's an actual variable. \s -> (s, s)
> defines a lambda function which takes any value, and returns a tuple
> with that value in both positions.
>
> So yes, get is point-free, but the missing argument is right there
> in-line. And yes, its type is simply implied from context.
>
>
> On Aug 1, 2017 4:17 PM, "Olumide" <[email protected] <mailto:[email protected]>>
> wrote:
>
> Ahoy Haskellers,
>
> In the section "Getting and Setting State"
> (http://learnyouahaskell.com/for-a-few-monads-more#state
> <http://learnyouahaskell.com/for-a-few-monads-more#state>) in LYH
> get is defined as
>
> get = state $ \s -> (s, s)
>
> How does does get determine the type s, is considering that it has
> no argument as per the definition given above? Or is the definition
> written in some sort of point-free notation where an argument has
> been dropped?
>
> I find the line stackNow <- get in the the function(?) stackyStack
> confusing for the same reason. I guess my difficulty is that state $
> \s ->(s , s) has a generic type (s) whereas the stackyStack has a
> concrete type. Is the type of s determined from the type of the
> stateful computation/do notation?
>
> Regards,
>
> - Olumide
> _______________________________________________
> Beginners mailing list
> [email protected] <mailto:[email protected]>
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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>
>
>
>
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------------------------------
Message: 2
Date: Tue, 01 Aug 2017 21:23:59 -0400
From: Atrudyjane <[email protected]>
To: Oliver Charles <[email protected]>
Cc: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Libraries for Playing Audio
Message-ID:
<FPuYdOyGakdgfmnGxyJgCIGCkaMZgcARB3C9152I1GfRtRppGlSsaeLbcn27-CBUPMMbnMkp7qqz38UWvhkYjrol5zZ_hz80eTDOC-x_NG0=@protonmail.com>
Content-Type: text/plain; charset="utf-8"
Hi Oliver,
The requirements are to play, pause play, and stop playing an mp3 file. Also
would like to use time elapsed and duration data.
Andrea
Sent with [ProtonMail](https://protonmail.com) Secure Email.
> -------- Original Message --------
> Subject: Re: [Haskell-beginners] Libraries for Playing Audio
> Local Time: August 1, 2017 4:01 AM
> UTC Time: August 1, 2017 9:01 AM
> From: [email protected]
> To: Atrudyjane <[email protected]>, The Haskell-Beginners Mailing
> List - Discussion of primarily beginner-level topics related to Haskell
> <[email protected]>, [email protected] <[email protected]>
> What are your requirements? SDL2's audio module is functional, but I don't
> know if it's sufficient for what you're looking for.
>
> On Tue, Aug 1, 2017 at 3:44 AM Atrudyjane <[email protected]> wrote:
>
>> Thanks Alexei,
>> Think I've narrowed it down to either sox or conduit-audio. Looks like
>> SDL-mixer hasn't been updated in a while and it has an 'All reported builds
>> failed' status as of 2015.
>> Regards,
>> Andrea
>>
>> Sent with [ProtonMail](https://protonmail.com) Secure Email.
>>
>>> -------- Original Message --------
>>> Subject: Re: [Haskell-beginners] Libraries for Playing Audio
>>> Local Time: July 31, 2017 12:50 AM
>>> UTC Time: July 31, 2017 5:50 AM
>>> From: [email protected]
>>> To: Atrudyjane <[email protected]>, The Haskell-Beginners Mailing
>>> List - Discussion of primarily beginner-level topics related to Haskell
>>> <[email protected]>
>>> There is haskell wrapper for powerful sox availiable also.
>>> http://hackage.haskell.org/package/sox
>>> Alexei
>>>> On 31 July 2017 at 07:09 Atrudyjane <[email protected]> wrote:
>>>>
>>>>
>>>> Hello Cafe,
>>>> Is there a recommended Haskell library for playing/manipulating audio
>>>> files? There"s a long list of sound libraries on Hackage, and was thinking
>>>> looking into either conduit-audio or SDL-mixer.
>>>> Thank You,
>>>> Andrea
>>>>
>>>> Sent with [ProtonMail](https://protonmail.com) Secure
>>>> Email._______________________________________________
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Message: 3
Date: Tue, 1 Aug 2017 19:26:57 -0700
From: Theodore Lief Gannon <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Grappling with State Monad get
Message-ID:
<cajopsud6ajw9bcmsipjmyucv8dli_f1pqny4y1c+p5spkz+...@mail.gmail.com>
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Actually, get is constrained immediately to be State Stack Stack. If later
statements tried to use it as something else, it would be a type error.
The types in a do block can only vary in their final parameter. The type of
stackyStack is State Stack (), so in that do block all the statements must
be forall a. State Stack a.
Now, check the type of get in GHCi:
get :: State a a
We know that the first type parameter here is Stack, and the second
position is the same type, thus State Stack Stack.
On Tue, Aug 1, 2017 at 5:13 PM, Olumide <[email protected]> wrote:
> Of course 's' is not a type variable as its lowercase.
>
> Therefore, get is a monad 'constructed' by the state function, correct?
>
> So, in the do notation the lambda is extracted and used as per the
> definition of bind. The context of which we speak therefore must derive
> from the next expression(?) in the do notation, which is somewhat confusing
> to determine in the example
>
> stackyStack :: State Stack ()
> stackyStack = do
> stackNow <- get
> if stackNow == [1,2,3]
> then put [8,3,1]
> else put [9,2,1]
>
> Regards,
>
> - Olumide
>
> On 02/08/17 00:35, Theodore Lief Gannon wrote:
>
>> 's' here is not a type variable, it's an actual variable. \s -> (s, s)
>> defines a lambda function which takes any value, and returns a tuple with
>> that value in both positions.
>>
>> So yes, get is point-free, but the missing argument is right there
>> in-line. And yes, its type is simply implied from context.
>>
>>
>> On Aug 1, 2017 4:17 PM, "Olumide" <[email protected] <mailto:[email protected]>>
>> wrote:
>>
>> Ahoy Haskellers,
>>
>> In the section "Getting and Setting State"
>> (http://learnyouahaskell.com/for-a-few-monads-more#state
>> <http://learnyouahaskell.com/for-a-few-monads-more#state>) in LYH
>> get is defined as
>>
>> get = state $ \s -> (s, s)
>>
>> How does does get determine the type s, is considering that it has
>> no argument as per the definition given above? Or is the definition
>> written in some sort of point-free notation where an argument has
>> been dropped?
>>
>> I find the line stackNow <- get in the the function(?) stackyStack
>> confusing for the same reason. I guess my difficulty is that state $
>> \s ->(s , s) has a generic type (s) whereas the stackyStack has a
>> concrete type. Is the type of s determined from the type of the
>> stateful computation/do notation?
>>
>> Regards,
>>
>> - Olumide
>> _______________________________________________
>> Beginners mailing list
>> [email protected] <mailto:[email protected]>
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>> <http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners>
>>
>>
>>
>>
>> _______________________________________________
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>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
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