From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
Subject: Re: Ada202X : Adding functors
Date: Fri, 16 Nov 2012 11:12:49 +0100
Date: 2012-11-16T11:12:47+01:00 [thread overview]
Message-ID: <50a6119f$0$9519$9b4e6d93@newsspool1.arcor-online.net> (raw)
In-Reply-To: <BLydnSqRNdU4GDjNRVn_vwA@giganews.com>
On 16.11.12 01:15, Peter C. Chapin wrote:
> val resultList = filter(myList, _ % 2 == 0)
Incidentally, I have just again had to turn a short expression
like this into a regular function, since keeping it as an
expression would have made the program unreadable.
I think that "growing up" to become a function is the fate of many
expressions playing the role of a function.
In the language I need to use, filtering looks like
my @resultList = grep { _ % 2 == 0 } @$myList;
Actually, I also need to sort records in $myList in reverse order by
a field named "id". Language support is structurally similar to
filtering. Special sort variables $a and $b provided by the language:
my @resultList = sort { $b->{"id"} <=> $a->{"id"} } @$myList;
Again, an unnamed expression, $b->{"id"} <=> $a->{"id"}.
It turned out at some point that the components of $myList needed a
more complex comparison, since "id" would not establish the desired
order. Therefore, the statement now is,
my @resultList = sort $by_latest @$myList;
where $by_latest is a code reference, a "function pointer". But! As
almost always, the function would not need to carry its environment
around.
So the situation made me end up with the Perl equivalent of a plain
old Ada generic or function pointer, roughly,
generic
type T(<>) is private;
with Comp (a, b: T) return int;
-- ...
function sort (items : in out List) return List;
This is not the first time that an expression had to become a function.
To me, this development seems to be the more frequent case.
Maybe unnamed expressions work much better in the role of a gimmick,
for example, when introducing "generic functions" by demonstration.
next prev parent reply other threads:[~2012-11-16 10:12 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-12 22:09 Ada202X : Adding functors Martin
2012-11-12 23:14 ` Jeffrey Carter
2012-11-12 23:19 ` Martin
2012-11-13 10:45 ` Georg Bauhaus
2012-11-13 12:08 ` Yannick Duchêne (Hibou57)
2012-11-13 12:35 ` Martin
2012-11-12 23:44 ` Adam Beneschan
2012-11-13 2:11 ` Jeffrey Carter
2012-11-13 11:11 ` Martin
2012-11-14 0:51 ` Adam Beneschan
2012-11-14 8:39 ` Martin
2012-11-14 16:54 ` Adam Beneschan
2012-11-14 18:54 ` Martin
2012-11-14 20:37 ` Dmitry A. Kazakov
2012-11-14 20:57 ` Shark8
2012-11-14 21:31 ` Martin
2012-11-14 22:42 ` Adam Beneschan
2012-11-15 9:27 ` Dmitry A. Kazakov
2012-11-14 21:45 ` Simon Wright
2012-11-14 22:22 ` Martin
2012-11-14 22:27 ` Martin
2012-11-13 4:22 ` Shark8
2012-11-15 0:20 ` sbelmont700
2012-11-15 7:12 ` Martin
2012-11-15 12:21 ` Georg Bauhaus
2012-11-15 12:31 ` Georg Bauhaus
2012-11-15 12:46 ` Martin
2012-11-16 6:15 ` Randy Brukardt
2012-11-15 10:11 ` Dmitry A. Kazakov
2012-11-15 15:52 ` Peter C. Chapin
2012-11-15 17:04 ` Dmitry A. Kazakov
2012-11-15 19:57 ` Georg Bauhaus
2012-11-15 20:39 ` Dmitry A. Kazakov
2012-11-16 0:15 ` Peter C. Chapin
2012-11-16 10:12 ` Georg Bauhaus [this message]
2012-11-16 0:01 ` Peter C. Chapin
2012-11-16 6:09 ` Randy Brukardt
2012-11-16 12:35 ` Peter C. Chapin
2012-11-16 18:10 ` Martin
2012-11-16 8:59 ` Dmitry A. Kazakov
2012-11-16 12:20 ` Peter C. Chapin
2012-11-16 17:44 ` Dmitry A. Kazakov
2012-11-18 15:58 ` Peter C. Chapin
2012-11-15 21:34 ` sbelmont700
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