Comments for Left Right Fold

Comment on The death of if-else, if, and else by EastZoneSoupCube - Linklist: Programming

EastZoneSoupCube - Linklist: Programming — Sat, 16 Jan 2010 15:48:48 +0000

[...] Left Right Fold: The death of if-else, if, and else [...]

Comment on The death of if-else, if, and else by Cihat

Cihat — Wed, 16 Dec 2009 07:20:25 +0000

This is also named as “Table Driven Method” in famous Code Complete 2 book.

Comment on The death of if-else, if, and else by HumbleMonkey

HumbleMonkey — Mon, 14 Dec 2009 16:24:40 +0000

The article is titled “The Death of If-else, if, and else”, and you use if, else if.
hmmmmm, and we are to take you advise seriously.

Comment on The death of if-else, if, and else by Twitted by delicious50

Twitted by delicious50 — Mon, 14 Dec 2009 13:23:21 +0000

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Comment on The death of if-else, if, and else by Twitted by karolk

Twitted by karolk — Mon, 14 Dec 2009 05:29:42 +0000

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Comment on The death of if-else, if, and else by Twitted by hackernws

Twitted by hackernws — Mon, 14 Dec 2009 05:08:58 +0000

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Comment on The death of if-else, if, and else by sshaw

sshaw — Tue, 08 Dec 2009 06:45:56 +0000

Oh wait, never mind… I missed the point

Comment on The death of if-else, if, and else by sshaw

sshaw — Tue, 08 Dec 2009 06:41:44 +0000

I agree that this is another good way to eliminate massive if-then-else in some cases, though I think the example would be better illustrated as:

var actions = {
    "football": function (channel)  { return true },
    "comedy" : function (channel) { return !channel.repeat },
    "crime" : function (channel)    { return (channel.showTitle != "Cops") }
};
 
function surf_dispatch(channels, actions) {
  for(var number in channels) {
   if(actions[channels[number].genre](channels[number])) {
     record(channels[number])
   }
  } 
}

Comment on The death of if-else, if, and else by Kumar

Kumar — Mon, 07 Dec 2009 09:50:17 +0000

Checkout “No ifs, ands or buts”, a presentation of the experimental “Subtext” programming environment explicitly built to tackle the problem you’re talking about.

http://subtextual.org/subtext2.html

Comment on The death of if-else, if, and else by Larry Battle

Larry Battle — Mon, 07 Dec 2009 03:07:00 +0000

What about something like this…
switch{ case (genre === "comedy" && !repeat): case (genre === "crime" && showTitle !== "Cops"): case (genre === "football"): record(channels[number]); }

Comment on The death of if-else, if, and else by More On The Death of If-Else

More On The Death of If-Else — Mon, 07 Dec 2009 02:27:18 +0000

[...] On The Death of If-Else Aaron Feng posted recently on “The death of if-else, if, and else”. In the post Aaron rewrote some JavaScript conditional checks using a dispatch table type [...]

Comment on The death of if-else, if, and else by Stylianos

Stylianos — Sun, 06 Dec 2009 23:12:34 +0000

I have been using this approach in php a lot and since javascript supports eval type of functionality you can also add dispatch information such that you can filter actions easier.

I am all pro this approach as a tabular format of action/reactions seems much more coherent and legible than nasty conditional tree. It is not that they magically disappear, but just that they don’t sit in the foreground

Comment on The death of if-else, if, and else by nbspnbsp

nbspnbsp — Sun, 06 Dec 2009 22:39:44 +0000

My vote is for using switch as well. Also double-spaces after periods? On the web?

Comment on The death of if-else, if, and else by Tom Janssens

Tom Janssens — Sun, 06 Dec 2009 20:19:08 +0000

Just a small suggestion: imho you should include all the fields in the decision table ( showname & repeat ), using lambda’s for example. Then you can avoid the much hated if’s in your example delegates.

Comment on The death of if-else, if, and else by leipie

leipie — Sun, 06 Dec 2009 19:14:10 +0000

I believe almost the same behavior can be obtained by using a switch with each case calling its own function. (A switch uses a sorts of jump table) This also solves the default actions issue. The only thing you need to type extra is the break statement. (Which is handy to leave out in some cases
Also anonymous functions scream code replication, so if you put normal functions references in your actions array It becomes even more similar to a switch. (I hate code replication

Comment on The death of if-else, if, and else by ClipperHouse | Logic as data

ClipperHouse | Logic as data — Sun, 06 Dec 2009 19:11:32 +0000

[...] This article demonstrates a pattern to avoid brittle if-then statements. The idea is that, instead of very long conditional branches, one encapsulates evaluation logic in a table of data. Each data item is a function containing an arbitrary piece of logic – code which runs after being passed to another function. When you need to add new conditional logic, you add a new item to the table – no code changes to your main algorithm. This is very extensible. [...]

Comment on The death of if-else, if, and else by The death of if-else, if, and else – Left Right Fold « Netcrema – creme de la social news via digg + delicious + stumpleupon + reddit

Sun, 06 Dec 2009 18:46:47 +0000

[...] The death of if-else, if, and else – Left Right Foldleftrightfold.com [...]

Comment on The death of if-else, if, and else by Torbjørn Marø

Torbjørn Marø — Sun, 06 Dec 2009 17:47:56 +0000

[edit of previous...]

My co-worker actually presented this pattern in a ziptalk on Friday - without knowing the name. I called it a kind of table method patter implementation, and it has also a lot in common with Strategy Pattern (it IS strategy pattern, without objects).

So dispatch pattern it is then. It shows up more and more in my own code (C# mostly), and makes the code much more maintainable.

Comment on The death of if-else, if, and else by Bram Stein

Bram Stein — Sun, 06 Dec 2009 17:14:26 +0000

I’ve been experimenting with functional pattern matching in JavaScript (see: http://www.bramstein.com/projects/jfun/).

Using my experiments, you could rewrite your code as follows:

<code>
  function record(channel) {
    console.log("recording channel: " + channel);
  }
 
  var surf = fun(
    [{genre: 'football', showTitle: _, repeat: _, station: _}, $, record],
    [{genre: 'comedy', showTitle: _, repeat: false, station: _}, $, record],
    [{genre: 'crime', showTitle: 'Cops', repeat: _, station: _}, $, record],
    [{genre: _, showTitle: _, repeat: _, station: _}, $, function () {}]
  );
 
  Object.forEach(channels, function (channel, number) {
    surf(channel, number);
  });

The last case in the pattern match is a catch-all to make the match exhaustive.

I’m not sure if implementing pattern matching on top of JavaScript is a good idea though. The syntax especially suffers. I’ve been thinking about moving the pattern matching into a preprocessor, but then it wouldn’t be JavaScript anymore

Comment on The death of if-else, if, and else by Aaron Feng

Aaron Feng — Sun, 06 Dec 2009 16:56:43 +0000

@mike a default action can be implemented with almost no effort. Maybe I can show that, so there will be no error if genre isn’t in the action table.