Using Decimal in matches is tricky because two equal values can have
different precision so that 42.0d != 42.00d. You can even have cases where
420d != 420d, because one has three digits of precision and the other only
two digits.
On Wed, Feb 8, 2017 at 10:20 AM, José Valim <jose.va...@plataformatec.com.br
> wrote:
> Yes, you need to parse the decimal at compile time, something like this:
>
> defmacro sigil_X(decimal, _) do
> Macro.escape Decimal.new decimal
> end
>
>
>
> *José Valim*
> www.plataformatec.com.br
> Skype: jv.ptec
> Founder and Director of R&D
>
> On Wed, Feb 8, 2017 at 8:39 AM, Wojtek Mach <woj...@wojtekmach.pl> wrote:
>
>> Yes that worked, thanks.
>>
>> For the record, at first I tried:
>>
>> defmacro sigil_X(str, _) do
>> quote do
>> Decimal.new(unquote(str))
>> end
>> end
>>
>> and it failed but with a similar error: cannot invoke remote function
>> Decimal.new/1 inside match
>>
>> However, when macro expands to struct (here, just hardcoding it to prove
>> the point)
>>
>> defmacro sigil_X(_str, _) do
>> quote do
>> %Decimal{coef: 1, exp: 0, sign: 1}
>> end
>> end
>>
>> it works well.
>>
>> W dniu środa, 8 lutego 2017 03:11:31 UTC+1 użytkownik José Valim napisał:
>>>
>>> You should be able to use inside matches if you make it a macro.
>>>
>>> On Wed, Feb 8, 2017 at 02:28 Wojtek Mach <woj...@wojtekmach.pl> wrote:
>>>
>>>> (sorry for digging up old topic)
>>>>
>>>> I would be open though to adding support for number sigils like 13.0d,
>>>>> 13.0f although we should also consider how numbers like rationals would
>>>>> play into that.
>>>>>
>>>>
>>>> Would the idea by that Elixir would allow doing a 13.0d sigil, and
>>>> Decimal (whether in core or separate library) implements that sigil?
>>>>
>>>> I think another advantage of including Decimal in core is exactly the
>>>> sigil. Then the inspect implementation could simply return "13.0d" instead
>>>> of "#Decimal<13.0>" which would make it copy-pasteable in editor/iex (since
>>>> it'd be a valid Elixir expression) which makes it extremely convenient for
>>>> actually working with it, debugging code that uses it etc. Another
>>>> advantage is using it is in match.
>>>>
>>>> Currently this isn't allowed:
>>>>
>>>> defmodule DecimalSigil do
>>>> def sigil_X(str, _) do
>>>> Decimal.new(str)
>>>> end
>>>> end
>>>>
>>>> import DecimalSigil
>>>> ~X[3] = Decimal.add(~X[1], ~X[2])
>>>>
>>>> cannot invoke remote function DecimalSigil.sigil_X/2 inside match
>>>>
>>>> # see: https://github.com/ericmj/decimal/issues/38
>>>>
>>>> Looks like custom sigils can't be used in matches, but built-in can.
>>>>
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>>> --
>>>
>>>
>>> *José Valim*
>>> www.plataformatec.com.br
>>> Skype: jv.ptec
>>> Founder and Director of R&D
>>>
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--
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