Rewrite without parenthesis

newer
Re: [Haskell-cafe] Using stringize...

older
Re: [Haskell-cafe] Using stringize...

Carl Petersen

18 Aug 2016 18 Aug '16

8:03 a.m.

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

Attachments:

attachment.html (text/html — 99 bytes)

Show replies by date

Francesco Ariis

18 Aug 18 Aug

8:14 a.m.

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

8:23 a.m.

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]

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. On Aug 18, 2016 5:19 AM, "Francesco Ariis" 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.

Francesco Ariis

8:28 a.m.

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

Ivan Lazar Miljenovic

6:26 p.m.

On 18 August 2016 at 22:29, 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]

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" 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.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com

Daniel Berecz

8:31 a.m.

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... Regards, Daniel On Thu, Aug 18, 2016 at 2:19 PM Francesco Ariis 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.

Carl Petersen

10:53 a.m.

Thanks everyone for the quick responses. Greatly appreciated. On Thursday, August 18, 2016 at 7:03:22 AM UTC-5, Carl Petersen wrote:

...

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

Thanks!

Richard A. O'Keefe

8:46 p.m.

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

19 Aug 19 Aug

9:15 a.m.

...

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

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 On 19/08/16 02:46, Richard A. O'Keefe wrote: head . tail $ [1, 2, 3] --) - -- Alexander alexander@plaimi.net https://secure.plaimi.net/~alexander -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCgAGBQJXtwZ7AAoJENQqWdRUGk8Bb00P/jhJoUQTh3dCCLqbJHGJm1+x Cvh+DOXMWoQyQcEvOh9u6DruqpnLRGgzcqDVzUOmqM2rwwkt7kznF7vzof5mCcXx UPb9W0X7OI6oMFmvg2Xp9gDxTcQinTfaLDyyKRZzRV5xj+On00xtso8SjriVh2HO ubzQLVs0kxt3irX+7orvz3JmHDiiVnfMVR6bC+TfJE7gnrIjtJH5jxkZP+Os10tC fHOEa0jhRY8E8BR9nbzOhcw2/3HZeQLSek3MIFxvAtgyYT67JprJwKwLbslGHcKV YS7kHL8BEOb+rJbIi3RHyVNwSnYi0hc0WkwrQo4CI7yr2HloAwewMuMPwMHjmNRS CAmWry4lVO+NFAaRnnVCLkXqxUjOKeIs3D5Fin0DTxgfetp245RuHuYiMTiGV/yf 0eSX2QjPf4sNFutOHbUdgwmyLwZJRUFxgdOt2cYQ/keRPSdARjG8vf83rriBqCkB QNbQgC3M1w8zQ4sSeHvQUtYHAPBjyj8JHpQ1yFfy8g3DNyr7950IXalGPHNwvqZJ HGILbKJfMb+bB0n0/9rzsFz8gdXKt/9JvysYEg6VP4TWUaNIhSNoKLGXQsNYLFMB QFYN+byKb4JQVnPT8ojRS7btBcs3m9oAfiu2d+4rK6z9x31TjPMNiQUcNp8Vlmvb Tb9wd51A4uJARO/eja3O =UMCW -----END PGP SIGNATURE-----