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RE: seq-some-p and nil

From: Drew Adams
Subject: RE: seq-some-p and nil
Date: Mon, 7 Sep 2015 01:06:51 -0700 (PDT)

> >> I also liked seq-some-p returning the matching element over cl-some
> >> returning the value returned by the predicate.
> >
> > But if the matched element is nil ...
> If the function is not supposed to return non-nil if an element is
> matched but the element itself, then would it be ok? OTOH there would be
> again no way to differentiate between no element found and nil being
> found in the sequence.

1. That's too big a weakness.  It means that `seq-some' cannot
be used as a predicate.  (Again, lose the suffix `-p' if the
return value is important as something other than a Boolean.)

2. You can return both the sequence element and the value of the
predicate applied to it, as a cons: (ELEMENT . VALUE).

If the element is nil then the return value is (nil . VALUE).

That gives you both kinds of info, at the cost of a cons and
the trouble to dig out what you need from the cons.

3. If you never care about the VALUE, you could just return a
cons with the sequence element.  For nil the return value
would then be (nil).

#2 sounds reasonable.

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