Using bound variables in a fun's function clause

[Vincent de Phily]

Hi all,

consider the following snipnet :

> #!/usr/bin/escript
> main([Arg1, Arg2]) ->
>     F = fun(Arg1) -> match;                                                                                                                                                                
>            (_) -> nomatch                                                                                                                                                                    
>         end,                                                                                                                                                                                
>     io:format("~p~n", [F(Arg2)]).

Compiling this (R13B04) will complain about
./test/funbind.es:3: Warning: variable 'Arg1' is unused
./test/funbind.es:4: Warning: variable 'Arg1' is unused
./test/funbind.es:4: Warning: variable 'Arg1' shadowed in 'fun'
and create a fun where Arg1 is unbound.

If I change the implementation to :
>    F = fun(Arg1_tmp) when Arg1_tmp == Arg1 -> match;                                                                                                                                        
>           (_) -> nomatch                                                                                                                                                                      
>        end,                                                                                                                                                                                
or even :
>    F = fun(Foo) ->
>                case Foo of
>                    Arg1 -> match;
>                    _ -> nomatch  
>                end
>        end,
I'll get the behavior I want (creating the fun with Arg1 bound) without any
compile warning.


Is this the expected behaviour ? If so, what's the rationale ? It's easy to
work around, but it is quite surprising.

--
Vincent de Phily
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[Ahmed Omar]

Hi Vincent,
Yes it's expected. It's about the variables scope
You can read more here:
http://www.erlang.org/doc/programming_examples/funs.html#id58554

On Mon, Oct 18, 2010 at 3:29 PM, Vincent de Phily <
[hidden email]> wrote:

> Hi all,
>
> consider the following snipnet :
>
> > #!/usr/bin/escript
> > main([Arg1, Arg2]) ->
> >     F = fun(Arg1) -> match;
> >            (_) -> nomatch
> >         end,
> >     io:format("~p~n", [F(Arg2)]).
>
> Compiling this (R13B04) will complain about
> ./test/funbind.es:3: Warning: variable 'Arg1' is unused
> ./test/funbind.es:4: Warning: variable 'Arg1' is unused
> ./test/funbind.es:4: Warning: variable 'Arg1' shadowed in 'fun'
> and create a fun where Arg1 is unbound.
>
> If I change the implementation to :
> >    F = fun(Arg1_tmp) when Arg1_tmp == Arg1 -> match;
> >           (_) -> nomatch
> >        end,
> or even :
> >    F = fun(Foo) ->
> >                case Foo of
> >                    Arg1 -> match;
> >                    _ -> nomatch
> >                end
> >        end,
> I'll get the behavior I want (creating the fun with Arg1 bound) without any
> compile warning.
>
>
> Is this the expected behaviour ? If so, what's the rationale ? It's easy to
> work around, but it is quite surprising.
>
> --
> Vincent de Phily
> Mobile Devices
> [phone]
> [phone]
>
> Warning
> This message (and any associated files) is intended only for the use of its
> intended recipient and may contain information that is confidential,
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--
Best Regards,
- Ahmed Omar
http://nl.linkedin.com/in/adiaa
Follow me on twitter
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[Vincent de Phily]

On Monday 18 October 2010 15:38:38 Ahmed Omar wrote:
> Hi Vincent,
> Yes it's expected. It's about the variables scope
> You can read more here:
> http://www.erlang.org/doc/programming_examples/funs.html#id58554

Ah, I really should have done my homework better and RTFM (I'll blame
tiredness). Thanks for the quick reply.
--
Vincent de Phily
Mobile Devices
[phone]
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