Ranges originally worked as you proposed but we changed it to the restrict
form we have today exactly because of the confusion that arose from the
fact ranges with floats cannot be enumerated as in Enum.to_list/2. This
meant that:
Enum.member?(1.5, 1..2) #=> true
but
Enum.to_list(1..2) #=> [1, 2]
and it also meant that:
Enum.member?(1.5, 1.0..2.0) #=> true
Enum.to_list(1.0..2.0) #=> raises
Those inconsistencies are not worth the small benefits.
*José Valim*
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D
On Wed, Feb 8, 2017 at 4:48 PM, <[email protected]> wrote:
> Right now when you write something like
>
> x in -1..1
>
> elixir compiles it to
>
> is_integer(x) and x >= -1 and x <= 1
>
>
> If we were to write
>
> x in Enum.to_list(-1..1)
>
> It would have the exact same effect (as x would have to be an int that is
> bigger than or equal to -1 and lesser than or equal to 1 to pass) which
> makes sense when we look at Ranges as being just a lazily-evaluated
> enumerable (like a Stream).
>
> But i think that we should consider a range (atleast in the context of an
> "in" operation) equal to a space. Right now if we were to check if a float
> is inside a range, it would always fail (which, again, makes sense if we
> see the Range as a lazy enum).
>
> What i propose is that elixir accepts floats when executing "in" for a
> range. I believe it semantically makes sense (as in "0.5 is a number in the
> -1..1 range ?" instead of "0.5 is inside the list of integer produced by
> the -1..1 range/sequence")
>
> So, tl;dr, changing Kernel's macro in_range_literal/3 to
>
> (is_integer(x) or is_float(x)) and increasing_compare(a, b, c)
>
>
> That way we can easily check things like
>
> def valid_probability?(val), do: val in 0..1
>
> def contains_enough_products(amount), do: is_integer(amount) and amount
> in 1..10
>
>
> Note that in the above example i shown that you explicitly checks if the
> value is integer when you want it to be, which i believe is not a bad
> side-effect to this proposal (and i think that it is not obvious that this
> is the default behaviour, specially because the documentation doesn't
> states that ranges won't succeed with floats)
>
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