# [erlang-questions] Order of evaluation of guards

Ivan Uemlianin ivan@REDACTED
Mon Jan 5 10:18:30 CET 2015

```The main thing is ; is applied first, so your guard was like:

(( N > 0, M > 0, N < 100) ; (M < 100))

Then the whole single expression is evaluated.

Ivan

--
festina lente

> On 5 Jan 2015, at 09:04, Martin Koroudjiev <mrtndimitrov@REDACTED> wrote:
>
> Hi, thanks. So the "and" (,) is evaluated first and since (,) is not
> short circuit  all will be replaced with true/false. And then the "or"
> will be evaluated.
>
>
>> On 1/5/2015 10:57 AM, Ivan Uemlianin wrote:
>> The last is correct according to your guards: M < 100. Perhaps you could try:
>>
>>  ... when N > 0, M > 0, N < 100;
>>          N > 0, M > 0, M < 100 -> ...
>>
>> Happy New Year!
>>
>> Ivan
>>
>> --
>> festina lente
>>
>>
>>> On 5 Jan 2015, at 08:51, Martin Koroudjiev <mrtndimitrov@REDACTED> wrote:
>>>
>>> Hello,
>>>
>>> First of all - Happy New Year!
>>>
>>> Suppose we have a function that accepts 2 integers and we want to react
>>> only when both integers are greater than 0 and one of them is less than 100:
>>>
>>> I tried:
>>> (dilbert@REDACTED)1> F = fun(N, M) when N > 0, M > 0, N < 100; M < 100
>>> -> cool; (_, _) -> not_cool end.
>>> #Fun<erl_eval.12.106461118>
>>> (dilbert@REDACTED)2> F(1,2).
>>> cool
>>> (dilbert@REDACTED)3> F(1,200).
>>> cool
>>> (dilbert@REDACTED)4> F(0,200).
>>> not_cool
>>> (dilbert@REDACTED)5> F(0,50).
>>> cool
>>>
>>> The last is not correct.
>>> What is the order of evaluation of the guards? Sadly parentheses are not
>>> allowed in guards.
>>>
>>> Best regards,
>>> Martin
>>>
>>> _______________________________________________
>>> erlang-questions mailing list
>>> erlang-questions@REDACTED
>>> http://erlang.org/mailman/listinfo/erlang-questions
>

```