Interesting style i haven't seen....
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Interesting style i haven't seen....
by Greg Smyth
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A friend just came up with this, and i thought it was pretty
interesting(arguments against doing this kind of thing in Erlang aside...) as I'd never seen this type of thing done before... Anyone care to shed some light on why/how this works:- %% -module(dog). -export([new/1, woof/1]). new(Name) -> {dog, Name}. woof(Self) -> {dog, Name} = Self, io:format("~p says 'woof!'~n", [Name]). %% % 13> c(dog). % {ok,dog} % 14> Dog = dog:new("Fido"). % {dog,"Fido"} % 15> Dog:woof(). % "Fido" says 'woof!' % ok Many thanks, Greg ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Dave Smith-10
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Is this a trick question? I feel like I'm missing something here... :)
If the confusion is re: the use of "new", remember that Erlang has no concept of objects or explicit allocation (like that anyways). D. On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> wrote: > A friend just came up with this, and i thought it was pretty > interesting(arguments against doing this kind of thing in Erlang > aside...) as I'd never seen this type of thing done before... > > Anyone care to shed some light on why/how this works:- > > %% > -module(dog). > -export([new/1, woof/1]). > > new(Name) -> {dog, Name}. > > woof(Self) -> > {dog, Name} = Self, > io:format("~p says 'woof!'~n", [Name]). > %% > > % 13> c(dog). > % {ok,dog} > > % 14> Dog = dog:new("Fido"). > % {dog,"Fido"} > > % 15> Dog:woof(). > % "Fido" says 'woof!' > % ok > > Many thanks, > Greg > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Chris Tilt
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It's the use of Dog:woof() that throws me. Dog is a variable and I don't understand the semantics of "Variable:function()".
Cheers, Chris On 10/30/09 9:32 AM, "Dave Smith" <dizzyd@...> wrote: Is this a trick question? I feel like I'm missing something here... :) If the confusion is re: the use of "new", remember that Erlang has no concept of objects or explicit allocation (like that anyways). D. On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> wrote: > A friend just came up with this, and i thought it was pretty > interesting(arguments against doing this kind of thing in Erlang > aside...) as I'd never seen this type of thing done before... > > Anyone care to shed some light on why/how this works:- > > %% > -module(dog). > -export([new/1, woof/1]). > > new(Name) -> {dog, Name}. > > woof(Self) -> > {dog, Name} = Self, > io:format("~p says 'woof!'~n", [Name]). > %% > > % 13> c(dog). > % {ok,dog} > > % 14> Dog = dog:new("Fido"). > % {dog,"Fido"} > > % 15> Dog:woof(). > % "Fido" says 'woof!' > % ok > > Many thanks, > Greg > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Adriano Bonat
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IIRC this is called parameterized modules :)
On Fri, Oct 30, 2009 at 2:32 PM, Dave Smith <dizzyd@...> wrote: > Is this a trick question? I feel like I'm missing something here... :) > > If the confusion is re: the use of "new", remember that Erlang has no > concept of objects or explicit allocation (like that anyways). > > D. > > On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> wrote: >> A friend just came up with this, and i thought it was pretty >> interesting(arguments against doing this kind of thing in Erlang >> aside...) as I'd never seen this type of thing done before... >> >> Anyone care to shed some light on why/how this works:- >> >> %% >> -module(dog). >> -export([new/1, woof/1]). >> >> new(Name) -> {dog, Name}. >> >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> %% >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % {dog,"Fido"} >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> >> Many thanks, >> Greg >> >> ________________________________________________________________ >> erlang-questions mailing list. See http://www.erlang.org/faq.html >> erlang-questions (at) erlang.org >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Greg Smyth
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Yeah,
It certainly wasn't a trick question, unless the trick is on me... :) I still dont get how:- Variable = {atom, Value}, Variable:function/0. then gets converted to a call to atom:function({atom, Value}) if that makes sense...? Cheers, Greg On Fri, Oct 30, 2009 at 4:36 PM, Chris Tilt <chris.tilt@...> wrote: > It’s the use of Dog:woof() that throws me. Dog is a variable and I don’t > understand the semantics of “Variable:function()”. > Cheers, Chris > > > On 10/30/09 9:32 AM, "Dave Smith" <dizzyd@...> wrote: > > Is this a trick question? I feel like I'm missing something here... :) > > If the confusion is re: the use of "new", remember that Erlang has no > concept of objects or explicit allocation (like that anyways). > > D. > > On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> wrote: >> A friend just came up with this, and i thought it was pretty >> interesting(arguments against doing this kind of thing in Erlang >> aside...) as I'd never seen this type of thing done before... >> >> Anyone care to shed some light on why/how this works:- >> >> %% >> -module(dog). >> -export([new/1, woof/1]). >> >> new(Name) -> {dog, Name}. >> >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> %% >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % {dog,"Fido"} >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> >> Many thanks, >> Greg >> >> ________________________________________________________________ >> erlang-questions mailing list. See http://www.erlang.org/faq.html >> erlang-questions (at) erlang.org >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Colm Dougan
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I think it works because
Dog:woof() means the same thing as : dog:woof(Dog) .. by virtue of the fact that Dog is a tuple with a first element of "dog". I seem to recall this is a consequence of the parametrized modules feature. Colm On Fri, Oct 30, 2009 at 4:25 PM, Greg Smyth <gsmyth@...> wrote: > A friend just came up with this, and i thought it was pretty > interesting(arguments against doing this kind of thing in Erlang > aside...) as I'd never seen this type of thing done before... > > Anyone care to shed some light on why/how this works:- > > %% > -module(dog). > -export([new/1, woof/1]). > > new(Name) -> {dog, Name}. > > woof(Self) -> > {dog, Name} = Self, > io:format("~p says 'woof!'~n", [Name]). > %% > > % 13> c(dog). > % {ok,dog} > > % 14> Dog = dog:new("Fido"). > % {dog,"Fido"} > > % 15> Dog:woof(). > % "Fido" says 'woof!' > % ok > > Many thanks, > Greg > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Adriano Bonat
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Exactly,
9> Blah = {modname, "arg1", "arg2", 3}. {modname,"arg1","arg2",3} 10> Blah:func(). ** exception error: undefined function modname:func/1 On Fri, Oct 30, 2009 at 2:45 PM, Colm Dougan <colm.dougan@...> wrote: > I think it works because > > Dog:woof() > > means the same thing as : > > dog:woof(Dog) > > .. by virtue of the fact that Dog is a tuple with a first element of > "dog". I seem to recall this is a consequence of the parametrized > modules feature. > > Colm > > On Fri, Oct 30, 2009 at 4:25 PM, Greg Smyth <gsmyth@...> wrote: >> A friend just came up with this, and i thought it was pretty >> interesting(arguments against doing this kind of thing in Erlang >> aside...) as I'd never seen this type of thing done before... >> >> Anyone care to shed some light on why/how this works:- >> >> %% >> -module(dog). >> -export([new/1, woof/1]). >> >> new(Name) -> {dog, Name}. >> >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> %% >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % {dog,"Fido"} >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> >> Many thanks, >> Greg >> >> ________________________________________________________________ >> erlang-questions mailing list. See http://www.erlang.org/faq.html >> erlang-questions (at) erlang.org >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Tony Arcieri
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On Fri, Oct 30, 2009 at 10:45 AM, Colm Dougan <colm.dougan@...> wrote:
> .. by virtue of the fact that Dog is a tuple with a first element of > "dog". I seem to recall this is a consequence of the parametrized > modules feature. > Note that the paramaterized modules paper: http://www.erlang.se/workshop/2003/paper/p29-carlsson.pdf ...specifies the value representing a paramaterized module is opaque. This is a side-effect of the implementation. That said, very interesting. -- Tony Arcieri Medioh/Nagravision |
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Re: Interesting style i haven't seen....
by Dave Smith-10
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I may be wrong, but I don't think this has anything to do with
parameterized modules, but is instead an old-school way of invoking functions. From the reference manual: "When applied to a number N of arguments, a tuple {Module,FunctionName} is interpreted as a fun, referring to the function FunctionName with arity N in the module Module. The function must be exported. This usage is deprecated. See Function Calls for an example." D. On Fri, Oct 30, 2009 at 11:15 AM, Tony Arcieri <tony@...> wrote: > On Fri, Oct 30, 2009 at 10:45 AM, Colm Dougan <colm.dougan@...> wrote: > >> .. by virtue of the fact that Dog is a tuple with a first element of >> "dog". I seem to recall this is a consequence of the parametrized >> modules feature. >> > > Note that the paramaterized modules paper: > > http://www.erlang.se/workshop/2003/paper/p29-carlsson.pdf > > ...specifies the value representing a paramaterized module is opaque. This > is a side-effect of the implementation. > > That said, very interesting. > > -- > Tony Arcieri > Medioh/Nagravision > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Bob Ippolito
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That's how parameterized modules work. An instance of a parameterized
module is a variable. This particular example is (ab)using an implementation detail of how parameterized modules are currently implemented. You'd get the same behavior with this module, which uses an actual parameterized module: ---- -module(dog, [Name]). -export([woof/0]). woof() -> io:format("~p says 'woof!'~n", [Name]). ---- 1> c(dog). {ok,dog} 2> Fido = dog:new(fido). {dog,fido} 3> Fido:woof(). fido says 'woof!' ok On Fri, Oct 30, 2009 at 12:36 PM, Chris Tilt <chris.tilt@...> wrote: > It's the use of Dog:woof() that throws me. Dog is a variable and I don't understand the semantics of "Variable:function()". > Cheers, Chris > > > On 10/30/09 9:32 AM, "Dave Smith" <dizzyd@...> wrote: > > Is this a trick question? I feel like I'm missing something here... :) > > If the confusion is re: the use of "new", remember that Erlang has no > concept of objects or explicit allocation (like that anyways). > > D. > > On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> wrote: >> A friend just came up with this, and i thought it was pretty >> interesting(arguments against doing this kind of thing in Erlang >> aside...) as I'd never seen this type of thing done before... >> >> Anyone care to shed some light on why/how this works:- >> >> %% >> -module(dog). >> -export([new/1, woof/1]). >> >> new(Name) -> {dog, Name}. >> >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> %% >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % {dog,"Fido"} >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> >> Many thanks, >> Greg >> >> ________________________________________________________________ >> erlang-questions mailing list. See http://www.erlang.org/faq.html >> erlang-questions (at) erlang.org >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Mihai Balea
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On Oct 30, 2009, at 1:22 PM, Dave Smith wrote: > "When applied to a number N of arguments, a tuple > {Module,FunctionName} is interpreted as a fun, referring to the > function FunctionName with arity N in the module Module. The function > must be exported. This usage is deprecated. See Function Calls for an > example." I've always wondered why that particular syntax quirk is being deprecated. I think it's neat. Mihai ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Nick Gerakines
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Yeah, not only can you have param'd modules but they can be extensions
of each other. http://gist.github.com/149735 --- begin nick.erl -module(nick, [City, State]). -export([city/0, state/0]). state() -> io:format("nick:state/0 -> ~p~n", [State]). city() -> io:format("nick:city/0 -> ~p ~n", [City]). --- end --- begin vanessa.erl -module(vanessa, [City, State]). -extends(nick). -export([city/0]). city() -> io:format("child:city/0 -> ~p ~n", [City]). --- end $ erlc nick.erl && erlc vanessa.erl 1> Me = nick:new("Mountain View", "CA"). {nick,"Mountain View","CA"} 2> Me:city(). nick:city/0 -> "Mountain View" ok 3> Me:state(). nick:state/0 -> "CA" ok 4> Vanessa = vanessa:new("Mountain View", "CA"). {vanessa,{nick,"Mountain View","CA"},"Mountain View","CA"} 5> Vanessa:city(). child:city/0 -> "Mountain View" ok 6> Vanessa:state(). nick:state/0 -> "CA" ok 7> On Fri, Oct 30, 2009 at 9:51 AM, Greg Smyth <gsmyth@...> wrote: > Looking at your example, I don't think this is parameterised modules > (although that is also interesting, thanks!). > > The confusing part (for me at least), is still the section:- > >> % 14> Dog = dog:new("Fido"). >> % ok >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' > > How does Value:function() - change into > > module:function(Value) > > when Value = {module, Something}) ? > > Cheers, > Greg > > On Fri, Oct 30, 2009 at 4:42 PM, Dale Harvey <harveyd@...> wrote: >> The syntax is a bit wrong, >> -module(dog, [Name]). >> -export([woof/1]). >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % ok >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> but erlang does support it, parameterised modules >> http://www.clickcaster.com/channel/tag/modules?channel=diveintoerlang >> 2009/10/30 Dave Smith <dizzyd@...> >>> >>> Is this a trick question? I feel like I'm missing something here... :) >>> >>> If the confusion is re: the use of "new", remember that Erlang has no >>> concept of objects or explicit allocation (like that anyways). >>> >>> D. >>> >>> On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> >>> wrote: >>> > A friend just came up with this, and i thought it was pretty >>> > interesting(arguments against doing this kind of thing in Erlang >>> > aside...) as I'd never seen this type of thing done before... >>> > >>> > Anyone care to shed some light on why/how this works:- >>> > >>> > %% >>> > -module(dog). >>> > -export([new/1, woof/1]). >>> > >>> > new(Name) -> {dog, Name}. >>> > >>> > woof(Self) -> >>> > {dog, Name} = Self, >>> > io:format("~p says 'woof!'~n", [Name]). >>> > %% >>> > >>> > % 13> c(dog). >>> > % {ok,dog} >>> > >>> > % 14> Dog = dog:new("Fido"). >>> > % {dog,"Fido"} >>> > >>> > % 15> Dog:woof(). >>> > % "Fido" says 'woof!' >>> > % ok >>> > >>> > Many thanks, >>> > Greg >>> > >>> > ________________________________________________________________ >>> > erlang-questions mailing list. See http://www.erlang.org/faq.html >>> > erlang-questions (at) erlang.org >>> > >>> > >>> >>> ________________________________________________________________ >>> erlang-questions mailing list. See http://www.erlang.org/faq.html >>> erlang-questions (at) erlang.org >>> >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Bob Ippolito
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It is parameterized modules, just not implemented correctly. The only
reason it behaves that way is because of how they happen to be implemented in current versions of erlang's VM and compiler. In some future version of erlang the example at the beginning of this thread is expected to no longer work. On Friday, October 30, 2009, Greg Smyth <gsmyth@...> wrote: > Looking at your example, I don't think this is parameterised modules > (although that is also interesting, thanks!). > > The confusing part (for me at least), is still the section:- > >> % 14> Dog = dog:new("Fido"). >> % ok >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' > > How does Value:function() - change into > > module:function(Value) > > when Value = {module, Something}) ? > > Cheers, > Greg > > On Fri, Oct 30, 2009 at 4:42 PM, Dale Harvey <harveyd@...> wrote: >> The syntax is a bit wrong, >> -module(dog, [Name]). >> -export([woof/1]). >> woof(Self) -> >> {dog, Name} = Self, >> io:format("~p says 'woof!'~n", [Name]). >> >> % 13> c(dog). >> % {ok,dog} >> >> % 14> Dog = dog:new("Fido"). >> % ok >> >> % 15> Dog:woof(). >> % "Fido" says 'woof!' >> % ok >> but erlang does support it, parameterised modules >> http://www.clickcaster.com/channel/tag/modules?channel=diveintoerlang >> 2009/10/30 Dave Smith <dizzyd@...> >>> >>> Is this a trick question? I feel like I'm missing something here... :) >>> >>> If the confusion is re: the use of "new", remember that Erlang has no >>> concept of objects or explicit allocation (like that anyways). >>> >>> D. >>> >>> On Fri, Oct 30, 2009 at 10:25 AM, Greg Smyth <gsmyth@...> >>> wrote: >>> > A friend just came up with this, and i thought it was pretty >>> > interesting(arguments against doing this kind of thing in Erlang >>> > aside...) as I'd never seen this type of thing done before... >>> > >>> > Anyone care to shed some light on why/how this works:- >>> > >>> > %% >>> > -module(dog). >>> > -export([new/1, woof/1]). >>> > >>> > new(Name) -> {dog, Name}. >>> > >>> > woof(Self) -> >>> > {dog, Name} = Self, >>> > io:format("~p says 'woof!'~n", [Name]). >>> > %% >>> > >>> > % 13> c(dog). >>> > % {ok,dog} >>> > >>> > % 14> Dog = dog:new("Fido"). >>> > % {dog,"Fido"} >>> > >>> > % 15> Dog:woof(). >>> > % "Fido" says 'woof!' >>> > % ok >>> > >>> > Many thanks, >>> > Greg >>> > >>> > ________________________________________________________________ >>> > erlang-questions mailing list. See http://www.erlang.org/faq.html >>> > erlang-questions (at) erlang.org >>> > >>> > >>> >>> ________________________________________________________________ >>> erlang-questions mailing list. See http://www.erlang.org/faq.html >>> erlang-questions (at) erlang.org >>> >> >> > > ________________________________________________________________ > erlang-questions mailing list. See http://www.erlang.org/faq.html > erlang-questions (at) erlang.org > > ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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Re: Interesting style i haven't seen....
by Robert Virding
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2009/10/30 Mihai Balea <mihai@...>
> > On Oct 30, 2009, at 1:22 PM, Dave Smith wrote: > > "When applied to a number N of arguments, a tuple >> {Module,FunctionName} is interpreted as a fun, referring to the >> function FunctionName with arity N in the module Module. The function >> must be exported. This usage is deprecated. See Function Calls for an >> example." >> > > I've always wondered why that particular syntax quirk is being deprecated. > I think it's neat. They are a remenent from the bad old days when erlang was less functional than it is today and we didn't have funs This was a hack and has no reason for existence now that we do have funs. Robert |
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Re: Interesting style i haven't seen....
by Tony Rogvall-2
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As already pointed out, this is new stuff, that has to do with
"abstract" modules (You can find it in beam_emu.c apply_last) The call corresponds to: apply({dog,"Fido"}, woof, []). As you can see it is not {dog,woof} ! This feature is just an implementation detail and may change. /Tony On 30 okt 2009, at 21.34, Robert Virding wrote: > 2009/10/30 Mihai Balea <mihai@...> > >> >> On Oct 30, 2009, at 1:22 PM, Dave Smith wrote: >> >> "When applied to a number N of arguments, a tuple >>> {Module,FunctionName} is interpreted as a fun, referring to the >>> function FunctionName with arity N in the module Module. The >>> function >>> must be exported. This usage is deprecated. See Function Calls for >>> an >>> example." >>> >> >> I've always wondered why that particular syntax quirk is being >> deprecated. >> I think it's neat. > > > They are a remenent from the bad old days when erlang was less > functional > than it is today and we didn't have funs This was a hack and has no > reason > for existence now that we do have funs. > > Robert ________________________________________________________________ erlang-questions mailing list. See http://www.erlang.org/faq.html erlang-questions (at) erlang.org |
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