And I'm afraid you've both lost me :(
Once upon a time I'd have been able to follow that discussion, but sadly not 
lately

"Warp" <war### [at] tagpovrayorg> wrote in message 
news:450e9b3d@news.povray.org...
> Mike Williams <nos### [at] econymdemoncouk> wrote:
>> a*b^c*d might mean different things depending on the order in which the
>> operators are applied
>
>  No, that's not the problem. The exponentiation operator as unambiguously
> a higher precedence than the multiplication operator and thus that
> expression is (well, should be) evaluated as a*(b^c)*d.
>
>  The problematic cases, however, are these two: -a^2 and a^b^c
>
>  In other words, is the precedence of the exponentiation operator lower
> or higher than the precedence of the unary minus in the base? And in the
> second case: Should the exponentiation operator be interpreted from
> left-to-right (as most other operators) or right-to-left?
>
>  The general consensus globally (ie. outside the POV world) is that
> the exponentiation operator should have higher precedence than the
> unary minus of the base. In other words, the first expression should
> be interpreted as "-(a^2)" and not as "(-a)^2".
>  Note that a unary minus in the exponent should, naturally, have a
> higher precedence so that expressions like "a^-2" will work.
>
>  As for the second expression, the general consensus seems to be
> that the exponentiation operator, unlike most other operators, should
> be interpreted from right-to-left. In other words, the second expression
> should be interpreted as "a^(b^c)". This is because it more intuitively
> represents how exponentiation (ie. superscript) works in mathematics.
>
>  The problem with POV-Ray is that it didn't follow either of these
> consensuses and this caused some complaints. The pov-team didn't want
> to get into a filosophical discussion about what is the correct way
> to interpret the ^ operator so they just removed it and now pow() is
> the only official way for exponentiation.
>
>  Note that it's only a question of agreement. It's not a question of
> technical difficulties. It is trivial to parse the ^ operator
> unambiguously with the precedence rules conforming to the global
> consensus (iow. it doesn't even require ugly hacks nor ugly exceptions
> in the parsing code, as long as the parsing code is already clean).
>
> -- 
>                                                          - Warp

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