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| richardc at csd.uu.se |
 Posted: Tue Mar 29, 2005 9:32 pm |
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Guest
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Mark Scandariato wrote:
> Interesting crash when compiling the following snippet:
>
> %%%----------------------
> -module(foo, [N]).
> -compile(export_all).
>
> bug(<<V:N/unit:8>>) -> V.
> %%%----------------------
>
> This is equivalent to:
> %%%----------------------
> -module(foo).
> -compile(export_all).
>
> bug(<<V:N/unit:8>>, {foo, N}) -> V.
> %%%----------------------
>
> Which would normally just complain that "variable 'N' is unbound".
Yes, this is a problem with the current implementation, which
expands the parameterized code just as you show; this means that
the variable N becomes bound too late to be used as an argument
to the binary-pattern (but in the case of the parameterized code,
we have already assured the compiler that N is bound, so it
happily passes it on to the backend, which crashes). For various
reasons (mainly efficiency), though, the THIS-variable needs to
be the last passed argument. The best solution for now is to
rewrite the code as
nobug(B) ->
case B of
<<V:N/unit:8>> -> V
end.
(until we can get the compiler to do this by itself). Probably
we should meanwhile complain about N being unbound.
/Richard
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| mscandar at cisco.com |
| Posted: Tue Mar 29, 2005 9:59 pm |
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Guest
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But even
foo(N, <<V:N/unit:8>>) -> V.
is illegal.
I assumed it had to do with the fact that order of paremeter evaluation isn't
guaranteed. (Unless I'm mistaken.)
Mark.
Richard Carlsson wrote:
> Mark Scandariato wrote:
>
>>Interesting crash when compiling the following snippet:
>>
>>%%%----------------------
>>-module(foo, [N]).
>>-compile(export_all).
>>
>>bug(<<V:N/unit:8>>) -> V.
>>%%%----------------------
>>
>>This is equivalent to:
>>%%%----------------------
>>-module(foo).
>>-compile(export_all).
>>
>>bug(<<V:N/unit:8>>, {foo, N}) -> V.
>>%%%----------------------
>>
>>Which would normally just complain that "variable 'N' is unbound".
>
>
> Yes, this is a problem with the current implementation, which
> expands the parameterized code just as you show; this means that
> the variable N becomes bound too late to be used as an argument
> to the binary-pattern (but in the case of the parameterized code,
> we have already assured the compiler that N is bound, so it
> happily passes it on to the backend, which crashes). For various
> reasons (mainly efficiency), though, the THIS-variable needs to
> be the last passed argument. The best solution for now is to
> rewrite the code as
>
> nobug(B) ->
> case B of
> <<V:N/unit:8>> -> V
> end.
>
> (until we can get the compiler to do this by itself). Probably
> we should meanwhile complain about N being unbound.
>
> /Richard
>
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| richardc at csd.uu.se |
| Posted: Tue Mar 29, 2005 11:14 pm |
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Guest
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Mark Scandariato wrote:
> But even
>
> foo(N, <<V:N/unit:8>>) -> V.
>
> is illegal.
You're right - moving the this-argument first wouldn't work either.
But the parameterized-module version *ought* to work (regardless of
how it is done under the hood), since the scope of the variable is
supposed to be the whole module. So it should be fixed, somehow.
/Richard
> Richard Carlsson wrote:
>
>> Mark Scandariato wrote:
>>
>>> Interesting crash when compiling the following snippet:
>>>
>>> %%%----------------------
>>> -module(foo, [N]).
>>> -compile(export_all).
>>>
>>> bug(<<V:N/unit:8>>) -> V.
>>> %%%----------------------
>>>
>>> This is equivalent to:
>>> %%%----------------------
>>> -module(foo).
>>> -compile(export_all).
>>>
>>> bug(<<V:N/unit:8>>, {foo, N}) -> V.
>>> %%%----------------------
>>>
>>> Which would normally just complain that "variable 'N' is unbound".
>>
>>
>>
>> Yes, this is a problem with the current implementation, which
>> expands the parameterized code just as you show; this means that
>> the variable N becomes bound too late to be used as an argument
>> to the binary-pattern (but in the case of the parameterized code,
>> we have already assured the compiler that N is bound, so it
>> happily passes it on to the backend, which crashes). For various
>> reasons (mainly efficiency), though, the THIS-variable needs to
>> be the last passed argument. The best solution for now is to
>> rewrite the code as
>>
>> nobug(B) ->
>> case B of
>> <<V:N/unit:8>> -> V
>> end.
>>
>> (until we can get the compiler to do this by itself). Probably
>> we should meanwhile complain about N being unbound.
>>
>> /Richard
>>
>
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