[ruby-talk:5880] Re: succ but no pred? (& the MURKY award)

Thanks Matz... see below.

In article <[e-mail]>,
  [e-mail] (Yukihiro Matsumoto) wrote:
> Hi,
>
> In message "[ruby-talk:5862] succ but no pred? (& the MURKY award)"
>     on 00/10/26, "Hal E. Fulton" <[e-mail]> writes:
>
> |Is there some special reason that Ruby has (here and there)
> |a successor function (succ) but never a predecessor function
> |(pred)?
>
> Two reasons:
>
>   * Perl does not have magic decrement
>
>   * I was (and still is) too tired to define what should be the exact
>     behavior of magic decrement myself.

OK... but for numbers it is trivial. Given an Integer#succ, should we
not have an Integer#pred also?

In fact, if we defined succ! and pred! also, these could serve as
preincrement and predecrement operators (++x, --x) which some C
programmers might miss. That is another issue. (There would still be no
"post" versions, but these are more problematic anyway.)

And as for decrementing strings -- my intuition (which may be wrong!)
says that it is no harder than incrementing... we would need to ensure
that x.succ.pred == x and x.pred.succ == x for all but the boundary
cases.

And there must be boundary cases. Just as there must be at least one
string that does not have a successor, likewise there must be at least
one string without a predecessor. (I am not sure about null strings.)

This is not a big deal for me... I have never used String#succ or
heard anyone else claim to use it.

But I do like to see regularity -- if Lightbulb#screw exists, I want
Lightbulb#unscrew to be there also. In fact, I think there are times
when we should say, "Both or neither! But not just one."

--
Hal Fulton


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