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"Fredrik Eriksson" <fe79}--at--{yahoo}--dot--{com> wrote in message
news:op.### [at] e6600 bredbandsbolagetse...
> On Wed, 09 Apr 2008 22:39:53 +0200, Orchid XP v8 <voi### [at] devnull> wrote:
>> Question: is "comelia" a word?
>
> "Comelia" is a name.
Ah, ok, so perhaps the lyrics went: "Karma, karma, karma Comelia"?
Very possible.
~Steve~
>
>
> --
> FE
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St. wrote:
> Ah, ok, so perhaps the lyrics went: "Karma, karma, karma Comelia"?
>
> Very possible.
>
> ~Steve~
Or "Karma Chameleon".
Wait, why am I admitting to remembering this song?
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Orchid XP v8 wrote:
>> Erlang has first-class functions as well as closures. Indeed, there
>> are warnings in the docs saying things like "take care if you store a
>> closure in a database that when you fetch it back out to run it,
>> you're running the same version of the interpreter." :-)
>
> Ooo. So much for "you can upgrade stuff in-place without shutting down".
> :-P
Heh. Well, you know, I don't think you can actually upgrade the
interpreter itself without shutting down the node you're running on. On
the other hand, you could in theory start up a new interpreter, ship the
running stuff over to it, then shut down the old one.
Upgrading without shutting anything down is easier when it's only Erlang
code you're upgrading, and not the VM itself, but you *can* do it with
enough forethought.
> [Mind you, persistent *closures*? That's got to be a fairly rarely used
> feature...]
Yah. That they even mention it boggles my mind.
> The I/O monad is unusual as monads go, but essentially the I/O functions
> return I/O command objects instead of actually *performing* I/O,
Yeah, that I figured out. I'm just trying to wrap my head around how
that would work with (say) the clock, or the status of whether your ISP
is currently screwy, or something like that, just in terms of
"referential transparency".
I'm trying to figure out conceptually how you represent "the clock" for
example in a way that it's "referentially transparent". Or can you not
actually do that, and that's the point of a monad?
--
Darren New / San Diego, CA, USA (PST)
"That's pretty. Where's that?"
"It's the Age of Channelwood."
"We should go there on vacation some time."
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"Sabrina Kilian" <"ykgp at vtSPAM.edu"> wrote in message
news:47fd76c4$1@news.povray.org...
> St. wrote:
> > Ah, ok, so perhaps the lyrics went: "Karma, karma, karma Comelia"?
>>
>> Very possible.
>>
>> ~Steve~
>
> Or "Karma Chameleon".
LOL! That's it!
> Wait, why am I admitting to remembering this song?
I know, I can't stand it either...
~Steve~
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>> [Mind you, persistent *closures*? That's got to be a fairly rarely
>> used feature...]
>
> Yah. That they even mention it boggles my mind.
5th rule of software design: If it's technically possible to use your
product in a certain way, somebody will try to actually use it that way.
You *know* this to be true! ;-)
>> The I/O monad is unusual as monads go, but essentially the I/O
>> functions return I/O command objects instead of actually *performing*
>> I/O,
>
> Yeah, that I figured out. I'm just trying to wrap my head around how
> that would work with (say) the clock, or the status of whether your ISP
> is currently screwy, or something like that, just in terms of
> "referential transparency".
>
> I'm trying to figure out conceptually how you represent "the clock" for
> example in a way that it's "referentially transparent". Or can you not
> actually do that, and that's the point of a monad?
I'm going to go with "you can't - hence the monad".
The "get time" function just returns an I/O command object. You can
replace that function call with the command object it returns and the
meaning of the program is left completely unchanged. Thus it is
referentially transparent.
The Haskell runtime actually *gets* the clock time, and it does this
theoretically "after" the Haskell code has already been run and
generated its giant command object, so...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Sabrina Kilian wrote:
> Or "Karma Chameleon".
> Wait, why am I admitting to remembering this song?
>:-D Hahahaha!
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Darren New wrote:
> There are strict rules, tho.
Looking down this list, it seems I'm aware of these on an instinctive
level. I certainly use commas according to these rules, although I've
never learnt these rules explicitly. Good to know!
>> Just don't get me started on apostrophes :)
>
> Angry Bob's Apostrophe Rules!
I'd say the 90% of apostrophe abuse would be avoided if people could
remember that apostrophes are never, ever, used for pluralising anything.
:)
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Invisible wrote:
> The "get time" function just returns an I/O command object. You can
> replace that function call with the command object it returns and the
> meaning of the program is left completely unchanged. Thus it is
> referentially transparent.
So if I assign the result of "get time" to a variable and use that
variable in multiple places, do I get the same time each place I use it,
or different times? I think that's what's confusing me.
S = get_time()
print(S)
do_long_task()
print(S)
I would think you *want* that to do something different from
print(get_time())
do_long_task()
print(get_time())
How would I write each of those in Haskell?
--
Darren New / San Diego, CA, USA (PST)
"That's pretty. Where's that?"
"It's the Age of Channelwood."
"We should go there on vacation some time."
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Darren New wrote:
> Invisible wrote:
>> The "get time" function just returns an I/O command object. You can
>> replace that function call with the command object it returns and the
>> meaning of the program is left completely unchanged. Thus it is
>> referentially transparent.
>
> So if I assign the result of "get time" to a variable and use that
> variable in multiple places, do I get the same time each place I use it,
> or different times? I think that's what's confusing me.
The key is "using".
Recall that the *only* way to *execute* an I/O action is to return it
from the "main" function. And, since you can only return a single
action, it's how you splice each mini-action into the giant-action
returned by "main" that counts. ;-)
If you splice in two copies of the self same action, that action gets
executed twice. It's that simple.
> S = get_time()
> print(S)
> do_long_task()
> print(S)
>
> I would think you *want* that to do something different from
> print(get_time())
> do_long_task()
> print(get_time())
>
> How would I write each of those in Haskell?
In Haskell, if you use the monadic "do" notation, then the syntax for
executing an action and putting its result into a variable is
do
...
x <- do_stuff
...
This is technically equivilent to
... do_stuff >>= \x -> ...
but less messy on paper. In your case, what you're trying to do is simply
do
t1 <- get_time
print t1
do_long_task
t2 <- get_time
print t2
as opposed to something like
do
s <- get_time
print s
do_long_task
print s
which just serves no useful purpose at all. Notice that it's the "<-"
that says "execute this *now*". In the second example, you only execute
the thing once, so it only happens once. It's really quite clear on paper.
In case you care, the desugared equivilents are:
get_time >>= \t1 -> (print t1 >> do_long_task >> get_time >>= \t2 ->
print t2))
and
get_time >>= \s -> (print s >> do_long_task >> print s)
You can see why people prefer the "do" notation...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> You can see why people prefer the "do" notation...
Yah. :-) I'll have to ponder this s'more.
--
Darren New / San Diego, CA, USA (PST)
"That's pretty. Where's that?"
"It's the Age of Channelwood."
"We should go there on vacation some time."
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