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Today's Topics:
1. Variable re-use (Shishir Srivastava)
2. Re: This year's Google Summer of Code (Shishir Srivastava)
3. Re: Variable re-use (Alexey Shmalko)
4. Re: Variable re-use (Grzegorz Milka)
5. Re: Variable re-use (Alexey Shmalko)
6. Re: This year's Google Summer of Code
(Sumit Sahrawat, Maths & Computing, IIT (BHU))
----------------------------------------------------------------------
Message: 1
Date: Tue, 28 Apr 2015 10:53:06 +0100
From: Shishir Srivastava <[email protected]>
To: beginners <[email protected]>
Subject: [Haskell-beginners] Variable re-use
Message-ID:
<cale5rtvstzqd0ngwtrmkxrddrykapozueaxjwupy888ruvn...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
Please can anyone explain how does 'a' get re-used in the code below. My
understanding so far of haskell is that variables are not allowed to mutate
or re-assigned.
---
do
a <- [1,2,3]
a <- [a+1]
return a
[2,3,4]
---
Thanks,
Shishir
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Message: 2
Date: Tue, 28 Apr 2015 11:11:02 +0100
From: Shishir Srivastava <[email protected]>
To: beginners <[email protected]>
Subject: Re: [Haskell-beginners] This year's Google Summer of Code
Message-ID:
<cale5rts+nl_azzynpzdxwxxhlmhnuik1ybwq5txvtcg37rs...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Brilliant work !
Congrats to ever so helpful Sumit Sahrawat !
Cheers,
Shishir
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Message: 3
Date: Tue, 28 Apr 2015 10:11:47 +0000
From: Alexey Shmalko <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Variable re-use
Message-ID:
<CAFC2PC6Eu_Okg455K_gKtoMWukx=pm77bhzg6dntquijrxi...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
If you rewrite your example without do notation, you'll get:
[1,2,3] >>= \a -> [a+1] >>= return a
You can notice that first `a` and the last one are different things. They
are just different bindings that happen to have the same name (You'll get
the shadowing warning if enable -Wall). They have nothing in common and can
have different types as well.
On Tue, Apr 28, 2015 at 12:53 PM Shishir Srivastava <
[email protected]> wrote:
> Hi,
>
> Please can anyone explain how does 'a' get re-used in the code below. My
> understanding so far of haskell is that variables are not allowed to mutate
> or re-assigned.
>
> ---
> do
> a <- [1,2,3]
> a <- [a+1]
> return a
>
> [2,3,4]
> ---
>
> Thanks,
> Shishir
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 4
Date: Tue, 28 Apr 2015 12:12:10 +0200
From: Grzegorz Milka <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Variable re-use
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"
Hi,
The variable is not reassigned, but hidden. The do notation is a
syntactic sugar for:
[1, 2, 3] >>= (\a ->
[a + 1] >>= (\a ->
return a))
The second 'a' is inside a nested lambda function and therefore inside a
nested scope. The first 'a' still exists, but the value to which it
refers is hidden inside the second lambda function, where 'a' is bound
to a different value.
On 28.04.2015 11:53, Shishir Srivastava wrote:
> Hi,
>
> Please can anyone explain how does 'a' get re-used in the code below. My
> understanding so far of haskell is that variables are not allowed to mutate
> or re-assigned.
>
> ---
> do
> a <- [1,2,3]
> a <- [a+1]
> return a
>
> [2,3,4]
> ---
>
> Thanks,
> Shishir
>
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
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Message: 5
Date: Tue, 28 Apr 2015 10:15:48 +0000
From: Alexey Shmalko <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Variable re-use
Message-ID:
<CAFC2PC6mZsxz=frse2v5qfnhs_ej3sz34xucoyh_1d1nwct...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I'm sorry, my example should've been:
[1,2,3] >>= \a -> [a+1] >>= \a -> return a
On Tue, Apr 28, 2015 at 1:12 PM Grzegorz Milka <[email protected]>
wrote:
> Hi,
>
> The variable is not reassigned, but hidden. The do notation is a syntactic
> sugar for:
>
> [1, 2, 3] >>= (\a ->
> [a + 1] >>= (\a ->
> return a))
>
>
> The second 'a' is inside a nested lambda function and therefore inside a
> nested scope. The first 'a' still exists, but the value to which it refers
> is hidden inside the second lambda function, where 'a' is bound to a
> different value.
>
> On 28.04.2015 11:53, Shishir Srivastava wrote:
>
> Hi,
>
> Please can anyone explain how does 'a' get re-used in the code below. My
> understanding so far of haskell is that variables are not allowed to mutate
> or re-assigned.
>
> ---
> do
> a <- [1,2,3]
> a <- [a+1]
> return a
>
> [2,3,4]
> ---
>
> Thanks,
> Shishir
>
>
>
>
> _______________________________________________
> Beginners mailing
> [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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------------------------------
Message: 6
Date: Tue, 28 Apr 2015 16:56:24 +0530
From: "Sumit Sahrawat, Maths & Computing, IIT (BHU)"
<[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] This year's Google Summer of Code
Message-ID:
<cajbew8oscsmc00garvjbei9sy81scdt+pcudymnckvtnd3p...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I am very humbled. Thanks, both of you.
My proposal is available at https://github.com/sumitsahrawat/gsoc, if
you're interested in knowing what I have planned to do.
On 28 April 2015 at 15:41, Shishir Srivastava <[email protected]>
wrote:
> Brilliant work !
>
> Congrats to ever so helpful Sumit Sahrawat !
>
> Cheers,
> Shishir
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
--
Regards
Sumit Sahrawat
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