Ruby Programming Language :: code problems


	code problems Hi, At Mon, 4 Jun 2007 12:36:50 +0900, david karapetyan wrote in [ruby-talk:254217]: > why is the following code not valid It is valid. > def fibber > a = 1 > b = 1 > lambda do > yield(a) > a,b = a+b,a > end > end irb(main):009:0> fib = fibber{\|x\|p x} => #<Proc:0xb7c63a74@(irb):4> irb(main):010:0> fib[] 1 => [2, 1] irb(main):011:0> fib[] 2 => [3, 2] irb(main):012:0> fib[] 3 => [5, 3] -- Nobu Nakada Hi, At Mon, 4 Jun 2007 13:25:50 +0900, david karapetyan wrote in [ruby-talk:254219]: > thanks. i didn't realize i had to provide the block as well when i was > creating the closure. i was hoping for a closure that could take a different > block every time. i wanted fib to be a function that had access to a and b > and every call to fib would require a block. as it is fib has its block > fixed at creation time. do you know of a way of doing what i wanted to do > originally? You need ruby 1.9. Block passing to a block isn't supported in 1.8. def fibber a = 1 b = 1 lambda do \|&block\| block.call(a) a,b = a+b,a end end irb(main):010:0> fib = fibber => #<Proc:b7ba2338@(irb):6> irb(main):011:0> 10.times {fib.call {\|x\|p x}} 1 2 3 5 8 13 21 34 55 89 => 10 -- Nobu Nakada On 6/3/07, Nobuyoshi Nakada <n@ruby-lang.org> wrote: - Hide quoted text - > Hi, > At Mon, 4 Jun 2007 13:25:50 +0900, > david karapetyan wrote in [ruby-talk:254219]: > > thanks. i didn't realize i had to provide the block as well when i was > > creating the closure. i was hoping for a closure that could take a different > > block every time. i wanted fib to be a function that had access to a and b > > and every call to fib would require a block. as it is fib has its block > > fixed at creation time. do you know of a way of doing what i wanted to do > > originally? > You need ruby 1.9. Block passing to a block isn't supported in > 1.8. > def fibber > a = 1 > b = 1 > lambda do \|&block\| > block.call(a) > a,b = a+b,a > end > end > irb(main):010:0> fib = fibber > => #<Proc:b7ba2338@(irb):6> > irb(main):011:0> 10.times {fib.call {\|x\|p x}} > 1 > 2 > 3 > 5 > 8 > 13 > 21 > 34 > 55 > 89 > => 10 > -- > Nobu Nakada I thought I read somewhere that 1.9 wasn't going to support closures. So it apparently does then? -- -fREW fREW wrote: > I thought I read somewhere that 1.9 wasn't going to support closures. You are thinking of continuations, not closures, maybe? IIRC, recent versions of YARV do not have closures. -- vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407 Joel VanderWerf wrote: > fREW wrote: >> I thought I read somewhere that 1.9 wasn't going to support closures. > You are thinking of continuations, not closures, maybe? > IIRC, recent versions of YARV do not have closures. Now I'm the one spreading confusion. To clarify: YARV does have closures YARV does not have continuations (at least in recent versions) Sorry... -- vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407 On 6/4/07, Joel VanderWerf <v@path.berkeley.edu> wrote: - Hide quoted text - > Joel VanderWerf wrote: > > fREW wrote: > >> I thought I read somewhere that 1.9 wasn't going to support closures. > > You are thinking of continuations, not closures, maybe? > > IIRC, recent versions of YARV do not have closures. > Now I'm the one spreading confusion. To clarify: > YARV does have closures > YARV does not have continuations (at least in recent versions) > Sorry... > -- > vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407 Isn't YARV supposed to be Ruby 1.9? Also, can someone explain the difference between closures and continuations? I thought they were the same thing. -- -fREW Hi, At Tue, 5 Jun 2007 02:58:20 +0900, Joel VanderWerf wrote in [ruby-talk:254306]: > Now I'm the one spreading confusion. To clarify: > YARV does have closures > YARV does not have continuations (at least in recent versions) YARV has continuations in the latest versions. -- Nobu Nakada On 6/4/07, Nobuyoshi Nakada <n@ruby-lang.org> wrote: > Hi, > At Tue, 5 Jun 2007 02:58:20 +0900, > Joel VanderWerf wrote in [ruby-talk:254306]: > > Now I'm the one spreading confusion. To clarify: > > YARV does have closures > > YARV does not have continuations (at least in recent versions) > YARV has continuations in the latest versions. Wow, congratulations, that must have been tough work! Robert -- You see things; and you say Why? But I dream things that never were; and I say Why not? -- George Bernard Shaw On 6/4/07, fREW <fri@gmail.com> wrote: > Also, can someone explain the > difference between closures and continuations? I thought they were > the same thing. http://talklikeaduck.denhaven2.com/articles/2007/06/05/closing-in-on-... -- Rick DeNatale On 6/6/07, Rick DeNatale <rick.denat@gmail.com> wrote: > On 6/4/07, fREW <fri@gmail.com> wrote: > > Also, can someone explain the > > difference between closures and continuations? I thought they were > > the same thing. > http://talklikeaduck.denhaven2.com/articles/2007/06/05/closing-in-on-... > -- > Rick DeNatale Hi Rick I am still struggeling with continuations :(, as a matter of fact I hoped that they would behave as described above, but they do not, it seems. When I execute the code from your blog def continuation i = 0 lola = nil callcc {\|cc\| puts "In callcc";lola = cc} puts "i is now #{i}" i += 1 lola end cont = continuation # point of looping cont.call http://rubyquiz.com/quiz70.html I just get an endless loop, do you have an explanation for it? I remember there was a Ruby Quiz http://rubyquiz.com/quiz70.html with an excellent solution of Jim Weirich. One day I thought I understood the mechanism and optimized one callcc away, boy I made a complete fool out of myself, you can find it on the archives, I am not going to give the link ;). Well, just confused... Cheers Robert -- You see things; and you say Why? But I dream things that never were; and I say Why not? -- George Bernard Shaw On 6/5/07, Rick DeNatale <rick.denat@gmail.com> wrote: > On 6/4/07, fREW <fri@gmail.com> wrote: > > Also, can someone explain the > > difference between closures and continuations? I thought they were > > the same thing. > http://talklikeaduck.denhaven2.com/articles/2007/06/05/closing-in-on-... > -- > Rick DeNatale When I first learned about closures I was like, "Weird..." But then I found a use for them and they are awesome. Continuations are even weirder. I like the groundhog day analogy. Imagine how the program feels! -- -fREW On 6/6/07, Robert Dober <robert.do@gmail.com> wrote: - Hide quoted text - > Hi Rick I am still struggeling with continuations :(, as a matter of > fact I hoped that they would behave as described above, but they do > not, it seems. > When I execute the code from your blog > def continuation > i = 0 > lola = nil > callcc {\|cc\| puts "In callcc";lola = cc} > puts "i is now #{i}" > i += 1 > lola > end > cont = continuation > # point of looping > cont.call > I just get an endless loop, do you have an explanation for it? Robert, you are right, it loops in ruby, but not in irb. I was trying to cook up a simple example and got hoist by irb's petard. What happens in ruby is that calling the continuation goes back to the method, which returns to the point before the cont.call and away we go again. Continuations normally aren't reused in the way I did in the example. I'm actually not sure why it works the way it does in irb. Here's a simpler example which shows the flow of control concept. rick@frodo:/public/rubyscripts$ cat testcontin.rb def continuation puts "Before callcc" callcc {\|cc\| puts "In callcc";return cc} puts "After callcc" end puts "Begin" cont = continuation puts "Got cont #{cont.inspect}" if cont cont.call puts "After call" end puts "All done" rick@frodo:/public/rubyscripts$ ruby testcontin.rb Begin Before callcc In callcc Got cont #<Continuation:0xb7de3840> After callcc Got cont nil All done -- Rick DeNatale My blog on Ruby http://talklikeaduck.denhaven2.com/ On 6/6/07, Rick DeNatale <rick.denat@gmail.com> wrote: <snip> > Robert, you are right, it loops in ruby, but not in irb. > I was trying to cook up a simple example and got hoist by irb's petard. > What happens in ruby is that calling the continuation goes back to the > method, which returns to the point before the cont.call and away we go > again. That confirms my limited understanding of it :) > Continuations normally aren't reused in the way I did in the example. > I'm actually not sure why it works the way it does in irb. Hmm maybe I can give some hint in my zenwalk ruby 1.8.6 irb it loops as well as in my Windows (one click installer) irb, do you use a special irb setup? - Hide quoted text - > Here's a simpler example which shows the flow of control concept. > rick@frodo:/public/rubyscripts$ cat testcontin.rb > def continuation > puts "Before callcc" > callcc {\|cc\| puts "In callcc";return cc} > puts "After callcc" > end > puts "Begin" > cont = continuation > puts "Got cont #{cont.inspect}" > if cont > cont.call > puts "After call" > end > puts "All done" > rick@frodo:/public/rubyscripts$ ruby testcontin.rb > Begin > Before callcc > In callcc > Got cont #<Continuation:0xb7de3840> > After callcc > Got cont nil > All done That is a good example I really like to build on it. Thanks. Maybe I might add one thing which took me some minutes to work out ;) the nil value for the cont variable comes from : puts "After call". Cheers Robert -- You see things; and you say Why? But I dream things that never were; and I say Why not? -- George Bernard Shaw On 6/6/07, Rick DeNatale <rick.denat@gmail.com> wrote: > On 6/6/07, Robert Dober <robert.do@gmail.com> wrote: > > That is a good example I really like to build on it. > > Thanks. > > Maybe I might add one thing which took me some minutes to work out ;) > > the nil value for the cont variable comes from : puts "After call". > Actually it comes from the puts "After callcc" as this change demonstrates; Stupid typo of mine, sorry R.