allow line break at operators

[Johann Hibschman]

Chris Angelico <rosuav at gmail.com> writes:

> Why is left-to-right inherently more logical than
> multiplication-before-addition? Why is it more logical than
> right-to-left? And why is changing people's expectations more logical
> than fulfilling them? Python uses the + and - symbols to mean addition
> and subtraction for good reason. Let's not alienate the mathematical
> mind by violating this rule. It would be far safer to go the other way
> and demand parentheses on everything.

I'm a clearly a fool for allowing myself to be drawn into this thread,
but I've been playing a lot recently with the APL-derivative language J,
which uses a right-to-left operator precendence rule.

Pragmatically, this is because J defines roughly a bajillion operators,
and it would be impossible to remember the precendence of them all, but
it makes sense in its own way.

If you read "3 * 10 + 7", using right-to-left, you get "three times
something".  Then you read more and you get "three times (ten plus
something)."  And finally, you get "3*(10+7)".  The prefix gives the
continuation for the rest of the calculation; no matter what you
substitute for X in "3*X", you will always just evaluate X, then multply
it by 3.  Likewise, for "3*10+X", no matter what X is, you know you'll
add 10 and multiply by 3.

This took me a while to get used to, but it's definitely a nice
property.  Not much to do with python, but I do like the syntax enough
that I've implemented my own toy evaluator for J-like expressions in
python, to get around the verbosity of some bits of numpy.

Regards,
Johann