Re: Operator precedence and unary minus

[Tim Hill <drtimhill@...>]

> On May 21, 2018, at 3:32 PM, Albert Chan <albertmcchan@yahoo.com> wrote:
> 
> 
>> - a%m - b%n ~= - b%n - a%m
>> It's looks very weird
> 
> Remove space between unary minus and variable,
> and some parenthesis, it does not look weird
> 
> (-a % m) - (b % n) ~= (-b % n) - (a % n)
> 
> You can do the same trick to make any expression weird:
> 
> a  *  b+c  *  d+e / a  ^  3*c
> 
>> I think it would be good to lower the priority of unary minus in Lua.
>> For example, unary minus may have the same priority as binary minus.
>> 
>> -- Egor
> 
> Even if the idea is sound, it is too late to fix precedence
> 
> Anyway, how can it parse simple x / -y ?
> 
> 

You also need to be careful with literals and metatables. Consider:

-a * b
-10 * b

The same result? But what if b has a __mul metamethod?

—Tim