[erlang-questions] checking for unbound?

[Edmond Begumisa]

 From your example, I think what you're looking for is pattern matching...

case mnesia:dirty_index_read(myTable, value, indexField) of
    [] -> do something;  % nothing was returned
    [E] -> do something with E;  % 1 item was returned
    [H|T] -> do something with H and T  % more than 1 item was returned
end.

- Edmond -


On Sun, 21 Nov 2010 01:18:03 +1100, Andy Kriger <andy.kriger@REDACTED>  
wrote:

> Is there a way to test if a variable is unbound?
>
> I thought I could do something clever like...
> [E|EL] = mnesia:dirty_index_read(myTable, value, indexField),
> if <E is unbound> -> do something; % nothing was returned
>   length(EL) > 0 -> do something; % more than 1 item was returned
>   <E matches pattern> -> do something; % a match was returned
>   true -> do something % whatever is left
> end
>
> But I don't see a way to make the first test.
>
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