[erlang-questions] how to create user-defined guards

mats cronqvist <>
Mon Apr 27 12:11:21 CEST 2009


"Ivan Carmenates Garcia" <> writes:

> Hi all,
>
> I have a problem if for example I have an mnesia cosult like this 
>
> get_students()->
>         F = fun()->
>                 mnesia:select(person_table, [{#person_table{
>                         id          ='$1',
>                         name     ='$2',
>                         group    ='$3',
>                         type      ='$4',
>                         id_card ='$5',
>                         user      ='$6'},
>                         [{'=:=', {is_student,'$4'}, true}],
>                         ['$_']}])
>         end,
>         mnesia:transaction(F).
>
> is_student(X)->
>         if X == "Estudiante"->
>                 true;
>         true->
>                 false
>         end.
>

  i don't know anything about this, but the obvious solution would be;

{'=:=', '$4', "Estudiante"} 

  right? or am i missing something?

  mats



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