Groups > comp.lang.java.programmer > #7985

Re: new Java lambda syntax

From	Joshua Cranmer <Pidgeot18@verizon.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: new Java lambda syntax
Date	2011-09-13 15:22 -0500
Organization	A noiseless patient Spider
Message-ID	<j4oe35$h0u$1@dont-email.me> (permalink)
References	(6 earlier) <tsdvj8-vbg.ln1@news.simpsonst.f2s.com> <j4jbgt$i60$1@dont-email.me> <j4m6o0$t69$1@dont-email.me> <j4meun$99r$1@dont-email.me> <j4o9rt$i0g$1@dont-email.me>

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On 9/13/2011 2:04 PM, Daniele Futtorovic wrote:
> Okay, so you can have a lambda returning a value? Steve Simpson's statement:
>
>> There's no (...) long jumps (break, continue, return, throw)
>
> seemed to contradict that, as did Tom's about the "Gafterist nonsense"
> (<3), seeing how Gafter et al.'s proposal contained return values, IIRC.

What this is referring to is that lambdas do not have non-local control 
flow (the so-called "long jump" -- think about C's setjmp/longjmp 
feature [1]). Lambdas are effectively "mini-functions", so I could have 
a lambda that looked like this:

(int[] x, int y) => {
   for (int i = 0; i < x.length; i++)
     if (x[i] == y) return i;
   return -1;
};

which would effectively be a method that looked like:
int searchList(int[] x, int y) {
   for (int i = 0; i < x.length; i++)
     if (x[i] == y) return i;
   return -1;
}

In other words, what was not accepted was the thing that pissed me off 
about some of the proposals, namely that any block of statements should 
do the exact same thing if you wrapped it with ((){/*insert stmt*/})() [2].

So this would return true:
boolean foo() {
   ((){ return true; })();
   return false;
}

Obviously, if you want to have more complex logic in the lambda for 
returning multiple values other than what you can do in a simple 
expression, you'd need some sort of syntax. The compromise then being 
discussed would make this method return false:
boolean foo() {
   ((){ return true })();
   return false;
}

...

It was at that point that I personally hated non-local control flow in 
closures, er, lambdas. [3]

[1] Actually, don't. It breaks so many things.
[2] This is, supposedly, Tennent's Correspondence Principle. I say 
supposedly since a google search only reveals results that are 
specifically brought up in reference to the closures debate in JS and Java.
[3] Actually, doing some more research for this posting, it struck me 
that the primary rationale for non-local control flow comes from the 
heritage of lambdas. Most of the time, lambdas are used in reference to 
functional programming paradigms, and in the purer functional languages, 
control flow is not done via explicit constructs but rather via specific 
function calls. So it's a list.forEach( { body of loop }) as opposed to 
a for (Element e : list) { body of loop }; in such languages, non-local 
control flow is more important. However, given that Java is more 
imperatively structured than functionally structured, non-local control 
flow is by means no natural, nor is it necessary to implement, so I 
would still stand by my claim that non-local control flow is not a 
feature that should be implemented in Java's version of lambdas. For 
example, C++11 appears to omit it in their version of lambdas...

-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth

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new Java lambda syntax markspace <-@.> - 2011-09-08 13:19 -0700
  Re: new Java lambda syntax Roedy Green <see_website@mindprod.com.invalid> - 2011-09-08 15:18 -0700
    Re: new Java lambda syntax Arne Vajhøj <arne@vajhoej.dk> - 2011-09-08 18:27 -0400
    Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-08 15:40 -0700
      Re: new Java lambda syntax Arne Vajhøj <arne@vajhoej.dk> - 2011-09-08 19:27 -0400
        Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-08 16:29 -0700
          Re: new Java lambda syntax Arne Vajhøj <arne@vajhoej.dk> - 2011-09-08 19:48 -0400
          Re: new Java lambda syntax Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-09-08 17:56 -0700
            Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-08 22:23 -0700
    Re: new Java lambda syntax "Nasser M. Abbasi" <nma@12000.org> - 2011-09-08 16:41 -0700
    Re: new Java lambda syntax Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-08 20:50 -0500
  Re: new Java lambda syntax bugbear <bugbear@trim_papermule.co.uk_trim> - 2011-09-09 09:33 +0100
  Re: new Java lambda syntax Tom Anderson <twic@urchin.earth.li> - 2011-09-10 14:48 +0100
    Re: new Java lambda syntax Steven Simpson <ss@domain.invalid> - 2011-09-10 16:17 +0100
      Re: new Java lambda syntax Tom Anderson <twic@urchin.earth.li> - 2011-09-11 13:06 +0100
        Re: new Java lambda syntax Steven Simpson <ss@domain.invalid> - 2011-09-11 17:18 +0100
          Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-11 11:08 -0700
            Re: new Java lambda syntax Steven Simpson <ss@domain.invalid> - 2011-09-11 20:14 +0100
              Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-11 14:08 -0700
              Re: new Java lambda syntax Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-11 17:07 -0500
                Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-11 16:18 -0700
                Re: new Java lambda syntax Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-09-13 02:00 +0200
                Re: new Java lambda syntax Arne Vajhøj <arne@vajhoej.dk> - 2011-09-12 20:59 -0400
                Re: new Java lambda syntax Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-12 21:24 -0500
                Re: new Java lambda syntax Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-09-13 21:04 +0200
                Re: new Java lambda syntax Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-13 15:22 -0500
                Re: new Java lambda syntax Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-09-13 23:25 +0200
                Re: new Java lambda syntax Tom Anderson <twic@urchin.earth.li> - 2011-09-13 21:29 +0100
                Re: new Java lambda syntax Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2011-09-13 23:26 +0200
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-13 20:25 -0400
                Re: new Java lambda syntax Tom Anderson <twic@urchin.earth.li> - 2011-09-15 21:58 +0100
                Re: new Java lambda syntax Joshua Cranmer <Pidgeot18@verizon.invalid> - 2011-09-13 21:36 -0500
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-13 22:49 -0400
                Re: new Java lambda syntax "supercalifragilisticexpialadiamaticonormalizeringelimatisticantations" <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-14 02:49 -0400
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-14 03:01 -0400
                Re: new Java lambda syntax "winkleMeister" <..00@00.00.00.1> - 2011-09-14 09:59 +0000
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-15 10:16 -0400
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-14 06:40 -0400
                Re: new Java lambda syntax supercalifragilisticexpialadiamaticonormalizeringelimatisticantations <supercalifragilisticexpialadiamaticonormalizeringelimatisticantations@averylongandannoyingdomainname.com> - 2011-09-15 10:16 -0400
                Re: new Java lambda syntax lightworker <etts@0n.org.null> - 2011-09-16 01:57 +0000
                Re: new Java lambda syntax thoolen <th00len@th0lenbot.thorium> - 2011-09-15 22:41 -0400
                Re: new Java lambda syntax Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-09-14 06:29 -0300
                Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-14 07:40 -0700
                Re: new Java lambda syntax Lew <lewbloch@gmail.com> - 2011-09-14 08:01 -0700
                Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-14 14:50 -0700
                Re: new Java lambda syntax Lew <lewbloch@gmail.com> - 2011-09-14 18:02 -0700
                Re: new Java lambda syntax BGB <cr88192@hotmail.com> - 2011-09-14 21:08 -0700

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