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From: "Chris Saunders" <saunders@wchat.on.ca>
Subject: Re: Software landmines (loops)
Date: 1998/09/02
Message-ID: <6sijck$sj$1@news1.worldchat.com>#1/1
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Date: 1998-09-02T00:00:00+00:00
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>There are situations where extraneous calls in the final loop iteration
>would not be so harmless.  For instance, suppose you wished to implement
>an 'out' function for a LIST class that generated strings of the form:
>
> "{}"    for an empty list
> "{A}"   for a list with one element "A"
> "{A, B}" for a list with two elements "A" and "B"
>        etc...
>
>In other words, separate the elements by commas, but only if there is
>more than one element.  Here's a first attempt at a solution:
>
>out: STRING is
>    do
>        Result := "{";
>        from
>            start
>        until
>            after
>        loop
>                Result.append (item.out)
>                Result.append (", ");
>                forth
>            end loop
>        end
>        Result.append ("}");
>    end
>
>Unfortunately, this is incorrect, because it places an extraneous comma
>after the last element.  To correct this, we could add a test within the
>body:


My suggestion:

out: STRING is
    do
        Result := "{";
        from
            start
        until
            after
        loop
                Result.append (item.out)
                Result.append (", ");
                forth
            end loop
        end
        Result.prune_all_trailing (',')
        Result.append ("}");
    end

In place of prune_all_trailing you could also use head (Result.count - 1)
Costs very little overhead and leaves you with a nice looking loop.

Regards
Chris Saunders
saunders@wchat.on.ca