[erlang-questions] Guards syntax for multiple values

[Loïc Hoguin]

I would second this. It would be great to be able to say "when Val in 
[a, b, c]" and that be translated to "when Val =:= a; Val =:= b; Val =:= 
c" automatically. It's just nicer to read and write.

And since strings are lists this would also work: 'when Val in 
"=!~._-"'. I have a lot of HTTP parsing code that would benefit from 
such a construct.

I suppose "when Val in [a, b, c], Flag =:= true" would have to be 
translated as "Val =:= a, Flag =:= true; Val =:= b, Flag =:= true; Val 
=:= c, Flag =:= true" as well, due to how ;/, work in guards.

Cheers,

On 23/03/2019 04:24, Florent Gallaire wrote:
> Hello everybody,
> 
> I'm not very experimented in Erlang but I read carefully books and
> official documention.
> 
> It seems to me that the guards syntax is not as good as it should be,
> i.e. too much verbose for multiple values.
> 
> do(val1) -> val1;
> do(val2) -> val2;
> do(val3) -> val3;
> do(val4) -> val4;
> do(val5) -> val5.
> 
> do(Val) when Val =:= val1; Val =:= val2; Val =:= val3; Val =:= val4;
> Val =:= val5 -> Val.
> 
> It's boring and error prone to write.
> 
> Has a "in tuple" syntax already be considered ? Something like :
> 
> do(Val) when Val in {val1, val2, val3, val4, val5} -> Val.
> 
> Cheers
> 
> Florent
> 

-- 
Loïc Hoguin
https://ninenines.eu