Rewrite without parenthesis

[Carl Petersen]

How do you rewrite head (tail [1,2,3]) without parenthesis.

Thanks!

[mukesh tiwari]

head . tail $ [1, 2, 3]

On 18 Aug 2016 22:03, "Carl Petersen" <cepe...@gmail.com> wrote:

How do you rewrite head (tail [1,2,3]) without parenthesis.

Thanks!

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[gansteed]

have a look at this page: http://learnyouahaskell.com/higher-order-functions#composition

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[Francesco Ariis]

On Thu, Aug 18, 2016 at 05:03:21AM -0700, Carl Petersen wrote:
> How do you rewrite head (tail [1,2,3]) without parenthesis.

Hello Carl, simply

λ> tail [1,2,3]
[2,3]

will do! Haskell is not a Lisp, no need to wrap expressions
around ().

[Francesco Ariis]

On Thu, Aug 18, 2016 at 02:14:26PM +0200, Francesco Ariis wrote:
> Hello Carl, simply
>
> λ> tail [1,2,3]
> [2,3]
>
> will do! Haskell is not a Lisp, no need to wrap expressions
> around ().

And you want to do away with pesky square brackets:

λ> tail $ enumFromTo 1 3
[2,3]

[Theodore Lief Gannon]

Francesco, you missed a piece. 'head' is part of the expression. :) What Carl is looking for is one or the other of these:

head $ tail [1,2,3]
-- or --
head . tail $ [1,2,3]

The first one is shorter and fine for inlining, but I generally prefer the second form... it helps intuition about eta reduction, refactoring, and additional composition.

[Daniel Berecz]

Hi,

Do you want to apply tail and then head on the list?

If so, you can write:

head $ tail [1, 2, 3]

Besides the dollar opeartor there is a dot (.) operator. You can read more here:

http://stackoverflow.com/questions/940382/haskell-difference-between-dot-and-dollar-sign

Regards,

Daniel

[Francesco Ariis]

On Thu, Aug 18, 2016 at 05:29:34AM -0700, Theodore Lief Gannon wrote:
> Francesco, you missed a piece. 'head' is part of the expression. :) What
> Carl is looking for is one or the other of these:
>
> head $ tail [1,2,3]
> -- or --
> head . tail $ [1,2,3]
>
> The first one is shorter and fine for inlining, but I generally prefer the
> second form... it helps intuition about eta reduction, refactoring, and
> additional composition.

Welp, silly me! :P

[James Brown]

head1 = head . tail

head1 [1, 2, 3]

or 

head.tail $ [1, 2, 3]

On Thu, Aug 18, 2016 at 8:03 AM, Carl Petersen <cepe...@gmail.com> wrote:

How do you rewrite head (tail [1,2,3]) without parenthesis.

Thanks!

[Carl Petersen]

Thanks everyone for the quick responses. Greatly appreciated.

[Elliot Cameron]

Don't neglect this option which many prefer "head $ tail [1, 2, 3]"

[Ivan Lazar Miljenovic]

On 18 August 2016 at 22:29, Theodore Lief Gannon <tan...@gmail.com> wrote:
> Francesco, you missed a piece. 'head' is part of the expression. :) What
> Carl is looking for is one or the other of these:
>
> head $ tail [1,2,3]
> -- or --
> head . tail $ [1,2,3]

Or for this specific use case, [1,2,3] !! 1 ==> (!!1) [1,2,3]

>
> The first one is shorter and fine for inlining, but I generally prefer the
> second form... it helps intuition about eta reduction, refactoring, and
> additional composition.
>
>
> On Aug 18, 2016 5:19 AM, "Francesco Ariis" <fa...@ariis.it> wrote:
>>
>> On Thu, Aug 18, 2016 at 05:03:21AM -0700, Carl Petersen wrote:
>> > How do you rewrite head (tail [1,2,3]) without parenthesis.
>>
>> Hello Carl, simply
>>
>> λ> tail [1,2,3]
>> [2,3]
>>
>> will do! Haskell is not a Lisp, no need to wrap expressions
>> around ().
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
>
>
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.

--
Ivan Lazar Miljenovic
Ivan.Mi...@gmail.com
http://IvanMiljenovic.wordpress.com

[Richard A. O'Keefe]

On 19/08/16 12:03 AM, Carl Petersen wrote:
> How do you rewrite head (tail [1,2,3]) without parenthesis.

s/parenthesis/parentheses/

There are several ways to do this, including [1,2,3] !! 1.
The more important question is "why"?

[Alexander Berntsen]

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On 19/08/16 02:46, Richard A. O'Keefe wrote:
>>> How do you rewrite head (tail [1,2,3]) without parenthesis.
> s/parenthesis/parentheses/

head . tail $ [1, 2, 3] --)

- --
Alexander
alex...@plaimi.net
https://secure.plaimi.net/~alexander
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[Michael Orlitzky]

On 08/18/2016 08:03 AM, Carl Petersen wrote:
> How do you rewrite head (tail [1,2,3]) without parenthesis.
>

case [1,2,3] of x1:x2:xs -> Just x2; otherwise -> Nothing