Re: [Haskell-cafe] Re: How to do this in FP way?
One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? If it was me btw, I'd take a stab at the problem being that each time we do something a time gets updated and we want to know how much time has passed since we last did something. I'd approach this by generating a lazy list of times at which we started doing something, and then generating a lazy list of time differences. Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How to do this in FP way?
Thomas Davie [EMAIL PROTECTED] wrote: One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? There's no difference, as you can't do time-accounting non-strict and still expect it to give meaningful results: I'm merely trying to be helpful. None of the other solutions allow for the IO Monad. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to do this in FP way?
On 16 Jun 2008, at 18:28, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? There's no difference, as you can't do time-accounting non-strict and still expect it to give meaningful results: I'm merely trying to be helpful. None of the other solutions allow for the IO Monad. Firstly, I'd phrase that differently -- the IO Monad doesn't allow for the other solutions -- the other solutions are the truly functional ones. Secondly, I'm curious as to why you think that the two are incompatible, are you saying that for any meaningful kind of computation we need to resort to IORefs? I'd strongly contest that idea. Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How to do this in FP way?
Thomas Davie [EMAIL PROTECTED] wrote: On 16 Jun 2008, at 18:28, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? There's no difference, as you can't do time-accounting non-strict and still expect it to give meaningful results: I'm merely trying to be helpful. None of the other solutions allow for the IO Monad. Firstly, I'd phrase that differently -- the IO Monad doesn't allow for the other solutions -- the other solutions are the truly functional ones. Secondly, I'm curious as to why you think that the two are incompatible, are you saying that for any meaningful kind of computation we need to resort to IORefs? I'd strongly contest that idea. We have to resort to IO actions to get the time, and to IORefs because we need to chain up different calls to getCurrentTime using the IO Monad. The rest of the program can work with whatever you like best. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to do this in FP way?
On Mon, 16 Jun 2008, Achim Schneider wrote: We have to resort to IO actions to get the time, and to IORefs because we need to chain up different calls to getCurrentTime using the IO Monad. The rest of the program can work with whatever you like best. Isn't (StateT s IO a) the cleaner alternative to IORef? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How to do this in FP way?
Henning Thielemann [EMAIL PROTECTED] wrote: On Mon, 16 Jun 2008, Achim Schneider wrote: We have to resort to IO actions to get the time, and to IORefs because we need to chain up different calls to getCurrentTime using the IO Monad. The rest of the program can work with whatever you like best. Isn't (StateT s IO a) the cleaner alternative to IORef? Yes. But then using one IORef in one place won't make your program harder to understand, using Monad transformers quite certainly will. Admittedly, I'm becoming dodgy. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to do this in FP way?
On 16 Jun 2008, at 19:24, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: On 16 Jun 2008, at 18:28, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? There's no difference, as you can't do time-accounting non-strict and still expect it to give meaningful results: I'm merely trying to be helpful. None of the other solutions allow for the IO Monad. Firstly, I'd phrase that differently -- the IO Monad doesn't allow for the other solutions -- the other solutions are the truly functional ones. Secondly, I'm curious as to why you think that the two are incompatible, are you saying that for any meaningful kind of computation we need to resort to IORefs? I'd strongly contest that idea. We have to resort to IO actions to get the time, and to IORefs because we need to chain up different calls to getCurrentTime using the IO Monad. The rest of the program can work with whatever you like best. And in what way is this incompatible with either FRP as pierre suggested, or with generating an infinite list of times at which we call the function, and scanning it to find the differences? Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How to do this in FP way?
Thomas Davie [EMAIL PROTECTED] wrote: On 16 Jun 2008, at 19:24, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: On 16 Jun 2008, at 18:28, Achim Schneider wrote: Thomas Davie [EMAIL PROTECTED] wrote: One half of all Haskell coders will tell you that mutable state isn't a good starting point to learn Haskell, the other half will tell you the same because they want to be cool kids, too. And the one left over will point out that he asked how to do this the FP way, not the imperative way? There's no difference, as you can't do time-accounting non-strict and still expect it to give meaningful results: I'm merely trying to be helpful. None of the other solutions allow for the IO Monad. Firstly, I'd phrase that differently -- the IO Monad doesn't allow for the other solutions -- the other solutions are the truly functional ones. Secondly, I'm curious as to why you think that the two are incompatible, are you saying that for any meaningful kind of computation we need to resort to IORefs? I'd strongly contest that idea. We have to resort to IO actions to get the time, and to IORefs because we need to chain up different calls to getCurrentTime using the IO Monad. The rest of the program can work with whatever you like best. And in what way is this incompatible with either FRP as pierre suggested, or with generating an infinite list of times at which we call the function, and scanning it to find the differences? Argh. I should not have copypasted that GLUT code, as it introduces IORefs not because they're 100% necessary but because that code is called back from C. My main point is that his task, if it is as simple as he described it, will stay imperative. My point also depends on that code being part of a main driver loop, as you see it in games: It's just the thing I instantly recognised in his code. Consider this: update :: MyState - Int - MyState draw :: MyState - IO () mainLoop :: MyState - Int - IO () mainLoop st old = do now - getTimeOfDay let td = now - old st' = update st td draw st' mainLoop st' now This, to my understanding of things, is imperative, although there's no IORef to be found. OTOH, recursing like this is the FP way to do it. mainLoop's arguments are variables to my eyes. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
答复: [Haskell-cafe] Re: How to do this in FP way?
Yes, that's it, State.
Thanks.
-邮件原件-
发件人: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 代表 Achim Schneider
发送时间: 2008年6月16日 12:01
收件人: haskell-cafe@haskell.org
主题: [Haskell-cafe] Re: How to do this in FP way?
Magicloud Magiclouds [EMAIL PROTECTED] wrote:
static int old;
int diff (int now) { /* this would be called once a second */
int ret = now - old;
old = now;
return ret;
}
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State - IdleCallback
idle state = do
t0 - get $ t state
t1 - get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) - get $ ballPos state
(bvx, bvy) - get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.
--
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
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答复: [Haskell-cafe] Re: How to do this in FP way?
I think if I do not use a state, and the function would be called for many
times, it would waste memory, if using something like loop, right?
-邮件原件-
发件人: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 代表 Achim Schneider
发送时间: 2008年6月16日 12:01
收件人: haskell-cafe@haskell.org
主题: [Haskell-cafe] Re: How to do this in FP way?
Magicloud Magiclouds [EMAIL PROTECTED] wrote:
static int old;
int diff (int now) { /* this would be called once a second */
int ret = now - old;
old = now;
return ret;
}
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State - IdleCallback
idle state = do
t0 - get $ t state
t1 - get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) - get $ ballPos state
(bvx, bvy) - get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.
--
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited.
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Re: [Haskell-cafe] Re: How to do this in FP way?
Magicloud [EMAIL PROTECTED] wrote:
I think if I do not use a state, and the function would be called for
many times, it would waste memory, if using something like loop,
right?
nope, at least not in general.
update :: MyState - Int - MyState
draw :: MyState - IO ()
mainLoop :: MyState - Int - IO ()
mainLoop st old = do
now - getTimeOfDay
let td = now - old
st' = update st td
draw st'
mainLoop st' now
runs in constant space. Look up tail recursion in wikipedia.
-邮件原件-
发件人: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 代表 Achim Schneider
发送时间: 2008年6月16日 12:01
收件人: haskell-cafe@haskell.org
主题: [Haskell-cafe] Re: How to do this in FP way?
Magicloud Magiclouds [EMAIL PROTECTED] wrote:
static int old;
int diff (int now) { /* this would be called once a second */
int ret = now - old;
old = now;
return ret;
}
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State - IdleCallback
idle state = do
t0 - get $ t state
t1 - get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) - get $ ballPos state
(bvx, bvy) - get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't
a good starting point to learn Haskell, the other half will tell you
the same because they want to be cool kids, too.
--
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
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答复: [Haskell-cafe] Re: How to do this in FP way?
But if there are some beautiful arithmetics that do not use something like
state, I won't say no to them.
-邮件原件-
发件人: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 代表 Achim Schneider
发送时间: 2008年6月16日 12:01
收件人: haskell-cafe@haskell.org
主题: [Haskell-cafe] Re: How to do this in FP way?
Magicloud Magiclouds [EMAIL PROTECTED] wrote:
static int old;
int diff (int now) { /* this would be called once a second */
int ret = now - old;
old = now;
return ret;
}
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State - IdleCallback
idle state = do
t0 - get $ t state
t1 - get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) - get $ ballPos state
(bvx, bvy) - get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.
--
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
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[Haskell-cafe] Re: How to do this in FP way?
Magicloud Magiclouds [EMAIL PROTECTED] wrote:
static int old;
int diff (int now) { /* this would be called once a second */
int ret = now - old;
old = now;
return ret;
}
You do it with variables, of course. This is out of some GLUT code,
using IORef's:
idle :: State - IdleCallback
idle state = do
t0 - get $ t state
t1 - get elapsedTime
t state $= t1
let td = fromIntegral t1 - fromIntegral t0
fps state $= 1/td * 1000
angle' state $~! (+2)
(bpx, bpy) - get $ ballPos state
(bvx, bvy) - get $ ballVel state
ballPos state $= (bpx + bvx*td, bpy + bvy*td)
postRedisplay Nothing
One half of all Haskell coders will tell you that mutable state isn't a
good starting point to learn Haskell, the other half will tell you the
same because they want to be cool kids, too.
--
(c) this sig last receiving data processing entity. Inspect headers for
past copyright information. All rights reserved. Unauthorised copying,
hiring, renting, public performance and/or broadcasting of this
signature prohibited.
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