[erlang-questions] Question about using case statements

Kostis Sagonas <>
Sat Aug 28 09:24:54 CEST 2010


James Aimonetti wrote:
> Hey list,
> 
> Wondered what the list thought of this usage of case statements: I
> have a file path and a proplist with some values, one of which tells
> me what to do with the file. I want to be sure the file exists before
> I do something with the file but didn't want to get too deep into
> nested case statements, so I have something like this ->
> 
> ...
> Prop = get_proplist_from_somwhere(),
> File = get_file_from_somewhere(),
> case filelib:is_regular(File) andalso get_value(key, Prop) of
>   false ->
>     handle_missing_file_error(File);
>   specific_value_1 ->
>     do_specific_value_1_action(File, Prop);
>   ...
>   _Val ->
>     io:format("Unhandled file action value ~p~n", [_Val]) % to be
> removed after testing
> end,
> ...
> 
> Is this common / acceptable use of the andalso short-circuit boolean?

It's something you can do alright, but it's not common.

I personally think that in this particular case it is unnecessary.  The 
following code expresses the code's intention much clearer, IMO:

...
File = get_file_from_somewhere(),
case filelib:is_regular(File) of
   false ->
     handle_missing_file_error(File);
   true ->
     Prop = get_proplist_from_somwhere(),
     case get_value(key, Prop) of
       specific_value_1 ->
         do_specific_value_1_action(File, Prop);
         ...
       _Val ->
         io:format("Unhandled file action value ~p~n", [_Val]) % to be
removed after testing
     end
end,
...

and it is not much more verbose.

Kostis


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