[erlang-questions] Re: If one guard expression in the guard fails, are the remaining expressions still evaluated?

Lukas Larsson <>
Sun Feb 20 17:11:27 CET 2011


The second sentance refers to the fact that if something in a guard throws an exception (i.e. fails) then the entire guard will fail. It does not refer to a guard statement returning false. If a guard statement does return false it will not continue executing if , are used, but it will of course do so if ; are used in the guard. You could of course skip the usage of , and ; and use andalso and orelse if you want control yourself of what will happen. 

Lukas
----- Original Message -----
From: "Alexey Romanov" <>
To: "Steve Davis" <>
Cc: 
Sent: Sunday, February 20, 2011 3:46:27 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna
Subject: Re: [erlang-questions] Re: If one guard expression in the guard fails, are the remaining expressions still evaluated?

I've asked precisely because reading section 7.24 didn't clarify it
for me. The relevant sentences are "The guard is true if all guard
expressions evaluate to true." and "If an arithmetic expression, a
boolean expression, a short-circuit expression, or a call to a guard
BIF fails (because of invalid arguments), the entire guard fails." The
first sentence suggests to me that all expressions are evaluated; the
second that expressions after the one that failed aren't. But both
aren't explicit.

I know about short-circuit expressions, but 7.14 doesn't say anything
about evaluation of guards (unsurprisingly).

Yours, Alexey Romanov



On Sun, Feb 20, 2011 at 4:31 PM, Steve Davis
<> wrote:
>
> Take a look at section 7.14 (Short-Circuit Expressions) as well as 7.24 of
> that chapter. It should clarify.
>
> /s
>
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