This code:
x+=x<0 and -100 or 100 |
doesn't work the way I'd expect; it sets x to either -100 or 100
I assume this happens because that line gets preprocessed to this:
x=x+x<0 and -100 or 100 |
which gets interpreted like this:
x=(x+x<0) and -100 or 100 |
but I wish it would be preprocessed to this instead:
x=x+(x<0 and -100 or 100) |
Here's a test cart; it currently (0.2.2c) fails the tests:
You can use a feature of the parser to find out what the final/unrolled code is:
> print([=[x+=x<0 and -100 or 100]=]) x = x + (x) <0 and -100 or 100 |
And yeah, this clearly doesn't unroll correctly, since it obviously needs to be this:
x = x + (x<0 and -100 or 100) |
It looks like the regex that @zep uses to search/replace the expression on the right side of the assignment is simply missing two of the comparison operators: "<" and ">".
Surprisingly, it does work correctly with other comparison operators:
> print([=[x+=x<=0 and -100 or 100]=]) x = x + (x<=0 and -100 or 100) > print([=[x+=x==0 and -100 or 100]=]) x = x + (x==0 and -100 or 100) > print([=[x+=x>=0 and -100 or 100]=]) x = x + (x>=0 and -100 or 100) |
So yes, there's a bug here.
As a workaround, you could enclose the expression manually:
> print([=[x+=(x<0 and -100 or 100)]=]) x = x + ((x<0 and -100 or 100 )) |
You could also flip the condition to use one of the working operators:
> print([=[x+=x>=0 and 100 or -100]=]) x = x + (x>=0 and 100 or -100) |
Or you could use the built-in sgn(x) function, which also compares x<0 and returns -1 or 1:
x=sgn(x)*100 |
(Note: Unlike C/C++'s sign(x), the PICO-8 sgn(x) does not return 0 when x==0. 0 is considered positive, so it returns 1.)
@StinkerB06
Ah, someone else told me. I forget, might have been Fred or maybe thisismypassword, maybe someone else. (I has swiss-cheese memory; I apologize to whomever deserves credit!) Edit: It was sam!
Aha! Yes indeed. All credit to sam for sharing the trick in the first place! :)
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