[erlang-questions] How to abstract out common receive clauses?

Torben Hoffmann <>
Fri May 6 13:21:41 CEST 2011


That will guard you from many lines of repetitive code!

On Fri, May 6, 2011 at 13:12, Ivan Uemlianin <> wrote:

> Thanks!  I knew there would be something.  Time for me to start using
> guards.
>
> Best wishes
>
> Ivan
>
>
>
> On 06/05/2011 11:54, Torben Hoffmann wrote:
>
>> -module(ivan).
>>
>> -compile(export_all).
>>
>>
>> process(This,That,State) ->
>>
>>    receive
>>    {From, do1} ->
>>        From ! do1,
>>        process(This,That,State);
>>    {From, do2 } ->
>>        From ! do2,
>>        process(This,That,State);
>>    {From, do3} when State=:=a ->
>>        From ! do3,
>>        process(This,That,b);
>>    {From, do4} when State=:=b ->
>>        From ! do4,
>>        process(This,That,a)
>>    end.
>>
>> listen(P) ->
>>    receive
>>    {send,M} ->
>>        P ! {self(),M},
>>        listen(P);
>>    M ->
>>        io:format("listen got: ~p~n",[M]),
>>        listen(P)
>>    end.
>>
>> Cheers,
>> Torben
>>
>>
>> On Fri, May 6, 2011 at 11:31, Ivan Uemlianin < <mailto:
>> >> wrote:
>>
>>    Dear All
>>
>>    % I have a process running continuously in a receive loop.  It
>>    should act slightly differently depending on one of its state
>>    parameters.  At the moment I have it like this:
>>
>>    process(This, That, a) ->
>>       receive
>>           {From, do1} ->
>>               do1,
>>               process(This, That, a);
>>           {From, do2} ->
>>               do2,
>>               process(This, That, a);
>>           {From, do3} ->
>>               do3,
>>               process(This, That, a)
>>       end;
>>
>>    process(This, That, b) ->
>>       receive
>>           {From, do1} ->
>>               do1,
>>               process(This, That, b);
>>           {From, do2} ->
>>               do2,
>>               process(This, That, b);
>>           {From, do4} ->
>>               do4,
>>               process(This, That, b)
>>       end.
>>
>>
>>    % Most of the receive clauses are common to both versions of
>>    process/3 (the real code is more complicated).  Is there a way to
>>    abstract out the common parts?  An "object oriented" language
>>    might use inheritance.  Prolog might use backtracking, perhaps a
>>    bit like this:
>>
>>    iProcess(This, That, a) ->
>>       receive
>>           {From, do3} ->
>>               do3,
>>               iProcess(This, That, a)
>>       end;
>>
>>    iProcess(This, That, b) ->
>>       receive
>>           {From, do4} ->
>>               do4,
>>               iProcess(This, That, b)
>>       end;
>>
>>    iProcess(This, That, Other) ->
>>       receive
>>           {From, do1} ->
>>               do1,
>>               iProcess(This, That, Other);
>>           {From, do2} ->
>>               do2,
>>               iProcess(This, That, Other)
>>       end.
>>
>>
>>    % A case would perhaps work, with the proviso that 'generic'
>>    receives would be evaluated first:
>>
>>    cProcess(This, That, Other) ->
>>       receive
>>           {From, do1} ->
>>               do1,
>>               cProcess(This, That, Other);
>>           {From, do2} ->
>>               do2,
>>               cProcess(This, That, Other)
>>       end,
>>       case Other of
>>           a ->
>>               receive
>>                   {From, do3} ->
>>                       do3,
>>                       cProcess(This, That, Other)
>>               end;
>>           b ->
>>               receive
>>                   {From, do4} ->
>>                       do4,
>>                       cProcess(This, That, Other)
>>               end
>>       end.
>>
>>
>>    % Is there a canonical way of dealing with this problem (other
>>    than copy-and-paste)?
>>
>>    With thanks and best wishes
>>
>>    Ivan
>>
>>    --     ============================================================
>>    Ivan A. Uemlianin
>>    Speech Technology Research and Development
>>
>>     <mailto:>
>>    www.llaisdy.com <http://www.llaisdy.com>
>>    llaisdy.wordpress.com <http://llaisdy.wordpress.com>
>>
>>    www.linkedin.com/in/ivanuemlianin
>>    <http://www.linkedin.com/in/ivanuemlianin>
>>
>>
>>       "Froh, froh! Wie seine Sonnen, seine Sonnen fliegen"
>>                        (Schiller, Beethoven)
>>    ============================================================
>>
>>    _______________________________________________
>>    erlang-questions mailing list
>>     <mailto:>
>>
>>    http://erlang.org/mailman/listinfo/erlang-questions
>>
>>
>>
>>
>> --
>> http://www.linkedin.com/in/torbenhoffmann
>>
>
>
> --
> ============================================================
> Ivan A. Uemlianin
> Speech Technology Research and Development
>
>                    
>                     www.llaisdy.com
>                         llaisdy.wordpress.com
>                     www.linkedin.com/in/ivanuemlianin
>
>    "Froh, froh! Wie seine Sonnen, seine Sonnen fliegen"
>                     (Schiller, Beethoven)
> ============================================================
>
>


-- 
http://www.linkedin.com/in/torbenhoffmann
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