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Today's Topics:
1. fnc explanation (sasa bogicevic)
2. Re: fnc explanation (Daniel Trstenjak)
3. Re: fnc explanation (Vale Cofer-Shabica)
4. Re: fnc explanation (sasa bogicevic)
----------------------------------------------------------------------
Message: 1
Date: Mon, 2 Jan 2017 18:05:57 +0100
From: sasa bogicevic <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] fnc explanation
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hi,
I have some trouble understanding the following function:
http://lpaste.net/350771
If someone can take the time and explain the part after WHERE clause that would
be great since I kind of know what the function does but have problems with the
param order for the go anonymous function.
Thanks, Sasa
{
name: Bogicevic Sasa
phone: +381606006200
}
------------------------------
Message: 2
Date: Mon, 2 Jan 2017 18:20:58 +0100
From: Daniel Trstenjak <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] fnc explanation
Message-ID: <20170102172058.GA28689@octa>
Content-Type: text/plain; charset=us-ascii
Hi Sasa,
> -- this confuses me, what is the _ here ? go is anonymous function, _ should
> stand for tuple ? and status xs from the top definition ?
> go _ status@(_, False) = status
The first argument of 'go' is '_', which means it's ignored.
The second argument is 'status@(_, False)'.
It's giving the tuple the name 'status' and pattern matching the tuple at once.
If the pattern match succeeds, then the tuple named 'status' is returned by 'go'
Greetings,
Daniel
------------------------------
Message: 3
Date: Mon, 2 Jan 2017 16:21:31 -0500
From: Vale Cofer-Shabica <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] fnc explanation
Message-ID:
<caazfv4q8c35ejoocbbwvgglfrpj7cbuqsnozewts2t+o-b+...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi Sasa,
It might also help to look at the type of foldr:
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
The function go has type:
go :: Ord a => a -> (Maybe a, Bool) -> (Maybe a, Bool)
The tuple, initially (Nothing, True), will be passed to go as its *2nd*
argument; the first argument will be an element of the list. The
underscore, which means match anything and throw it away, is there because
we don't care about any of the other elements once we know the list is not
ordered.
Hope that helps,
vale
--
vale cofer-shabica
401.267.8253
On Mon, Jan 2, 2017 at 12:20 PM, Daniel Trstenjak <
[email protected]> wrote:
>
> Hi Sasa,
>
> > -- this confuses me, what is the _ here ? go is anonymous function, _
> should stand for tuple ? and status xs from the top definition ?
> > go _ status@(_, False) = status
>
> The first argument of 'go' is '_', which means it's ignored.
>
> The second argument is 'status@(_, False)'.
> It's giving the tuple the name 'status' and pattern matching the tuple at
> once.
>
> If the pattern match succeeds, then the tuple named 'status' is returned
> by 'go'
>
>
> Greetings,
> Daniel
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 4
Date: Mon, 2 Jan 2017 23:59:36 +0100
From: sasa bogicevic <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] fnc explanation
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Thanks!
I had to look at it multiple times to get it but it is clear now. It is still
not intuitive for me since I come from imperative language world but I guess
time heals all :)
Thanks once again!
Sasa
Sasa Bogicevic
{
phone: +381606006200
}
> On Jan 2, 2017, at 22:21, Vale Cofer-Shabica <[email protected]>
> wrote:
>
> Hi Sasa,
>
> It might also help to look at the type of foldr:
> foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
>
> The function go has type:
> go :: Ord a => a -> (Maybe a, Bool) -> (Maybe a, Bool)
>
> The tuple, initially (Nothing, True), will be passed to go as its *2nd*
> argument; the first argument will be an element of the list. The underscore,
> which means match anything and throw it away, is there because we don't care
> about any of the other elements once we know the list is not ordered.
>
> Hope that helps,
> vale
>
>
> --
> vale cofer-shabica
> 401.267.8253
>
>> On Mon, Jan 2, 2017 at 12:20 PM, Daniel Trstenjak
>> <[email protected]> wrote:
>>
>> Hi Sasa,
>>
>> > -- this confuses me, what is the _ here ? go is anonymous function, _
>> > should stand for tuple ? and status xs from the top definition ?
>> > go _ status@(_, False) = status
>>
>> The first argument of 'go' is '_', which means it's ignored.
>>
>> The second argument is 'status@(_, False)'.
>> It's giving the tuple the name 'status' and pattern matching the tuple at
>> once.
>>
>> If the pattern match succeeds, then the tuple named 'status' is returned by
>> 'go'
>>
>>
>> Greetings,
>> Daniel
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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