Re: How to understand chapter 6 of Higher Order Perl?

It doesn't help that the examples are really boring and kind of obfuscated. For instance: sub promise(&) { $_[0] } That's right, that thing does nothing. I find this really annoying.

It doesn't "do nothing". It constructs a 'promise' from an anonymous block.

That is, it takes an anonymous block of code and returns a code reference to it, so that it can be executed at sometime in the future:


sub promise(&) { $_[0] };;
...
$later = promise{ say 'Keeping my' };;
...
$later->();; ## or just &$later;;
Keeping my
[download]

In other words, it constructs a callback.

To create an 'infinite' stream of values starting at 123 and incrementing by 2:

sub countFromBy{ my( $from, $step ) = @_; return promise{ $from += $st
+ep } };;
...
$counter = countFromBy( 123, 2 );;
...
say &$counter for 1 .. 10;;
125
127
129
131
133
135
137
139
141
143
[download]

Maybe that clarifies things a little for you?

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re: How to understand chapter 6 of Higher Order Perl? Select or Download Code

Replies are listed 'Best First'.
Re^2: How to understand chapter 6 of Higher Order Perl? by McA (Priest) on Mar 13, 2014 at 08:44 UTC
May I add somthing? The book says that this is "syntactic sugar". So, BrowserUk's example is the same as: `$later = sub { say 'Keeping my' }; ... $later->();` [download] McA	[reply] [d/l]
Re^2: How to understand chapter 6 of Higher Order Perl? by Anonymous Monk on Mar 13, 2014 at 09:00 UTC
Nah, I actually understand what it does (which is nothing useful). I just find it very annoying. That's not the real problem, of course. The problem is that I need some kind of tool or something to track all these function calls. So far I'm doing it manually, and that's kind of difficult when there is stuff like `my $hamming; $hamming = node(1, promise { merge(scale($hamming, 2), merge(scale($hamming, 3), scale($hamming, 5), )) } );` [download] I find it kind of unreadable even without promise.	[reply] [d/l]
Re^3: How to understand chapter 6 of Higher Order Perl? by BrowserUk (Patriarch) on Mar 13, 2014 at 10:52 UTC
Nah, I actually understand what it does (which is nothing useful). I just find it very annoying. I don't disagree with you. That's not the real problem, of course. The problem is that I need some kind of tool or something to track all these function calls. So far I'm doing it manually, and that's kind of difficult when there is stuff like ... I find it kind of unreadable even without promise. Again, I don't disagree. I call it obfuscation through over-encapsulation. The misguided attempt to gloss over moderately "difficult" perl syntax with myriad small, trivial named subroutines or methods. All it does is obscure the underlying algorithm; complicate maintenance and debugging; and throw performance to the dogs of dogma. This is far simpler, clearer and way more efficient. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^4: How to understand chapter 6 of Higher Order Perl? by Anonymous Monk on Mar 13, 2014 at 11:31 UTC
This is far simpler, clearer and more efficient You're right. And "syntax with myriad small ... subroutines" is not good for me at all. Especially when many of these subroutines tell that they're called __ANON__. I'll do as the fellow Anonimous Monk recommended. Thanks everyone.	[reply]
Re^3: How to understand chapter 6 of Higher Order Perl? by Anonymous Monk on Mar 13, 2014 at 09:13 UTC
time for a week long break?	[reply]
Re^4: How to understand chapter 6 of Higher Order Perl? by Anonymous Monk on Mar 13, 2014 at 09:20 UTC
I dunno, maybe this functional thing is simply too difficult to learn for what it does? It's not like I'm going to use it in real world. Perl is already write-only, heh.	[reply]
Re^5: How to understand chapter 6 of Higher Order Perl? by DrHyde (Prior) on Mar 13, 2014 at 11:18 UTC
Re^6: How to understand chapter 6 of Higher Order Perl? by Laurent_R (Canon) on Mar 13, 2014 at 23:18 UTC
Some notes below your chosen depth have not been shown here
Re^5: How to understand chapter 6 of Higher Order Perl? by Anonymous Monk on Mar 13, 2014 at 09:39 UTC


Your skill will accomplish what the force of many cannot
	PerlMonks