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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: stopping a loop iteration without exiting it
Date: Fri, 5 Jan 2018 17:58:31 -0600
Organization: JSA Research & Innovation
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Date: 2018-01-05T17:58:31-06:00
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Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> wrote in message 
news:p2o0mp$brp$1@dont-email.me...
...
> I've never written a spam filter, but I'd imagine that one would be 
> structured something like
>
> All_Msgs : loop
>    exit All_Msgs when Msg_Source.Is_Empty;
>
>    Msg := Msg_Source.Get;
>    Is_Spam := False;
>
>    All_Patterns : for Pattern of Patterns loop
>       Is_Spam := Pattern.Check (Msg);
>
>       if Is_Spam then
>          Reject (Message => Msg);
>
>          exit All_Patterns;
>       end if;
>    end loop All_Patterns;
>
>    if not Is_Spam then
>       Allow (Message => Msg);
>    end if;
> end loop All_Msgs;
>
> and moving on to the next pattern would be "return False;" in Check. 
> Reality is probably more complex than this.

Definitely. There are a number of different dispositions (Block [don't 
accept the message in the first place, not possible in this part of  the 
algorithm], Delete, Quarantine [for human inspection], or Allow). One also 
has to deal with white lists, and the possibility that a pattern might cause 
a white list trigger. I also have two levels of white list (allow 
unconditionally, or allow but quarantine questionable mail). And there are 
patterns specifically for different parts of the message (the text, the HTML 
markup, links, headers, etc.) Plus there are actions associated with the 
success or failure of certain patterns (such as checking linked websites for 
known spam sites). I've probably missed some cases, too.

                              Randy.