Re: Can LPeg parse PNG?

[Dirk Laurie <dirk.laurie@...>]

2016-12-10 15:09 GMT+02:00 KHMan <keinhong@gmail.com>:
> On 12/10/2016 7:18 PM, Soni L. wrote:
>>
>> On 10/12/16 12:12 AM, KHMan wrote:
>>>
>>> On 12/10/2016 9:46 AM, Duncan Cross wrote:
>>>>
>>>> On Sat, Dec 10, 2016 at 12:10 AM, Soni L. wrote:
>>>>>
>>>>> I was told PNG is a regular language, in the sense that you
>>>>> can validate any
>>>>> PNG chunk with a VERY VERY VERY LONG regex.
>>>>
>>>>
>>>> Including the 32-bit CRC at the end of the chunk? That's got to
>>>> be a
>>>> hell of a regex.
>>>
>>>
>>> I'm really curious about the "I was told PNG is a regular
>>> language" though. It directs the blame for the idea on an
>>> anonymous someone else.
>>>
>>> Perhaps he has VERY VERY VERY LARGE amounts of free time this
>>> weekend, or perhaps he wants to trap some unsuspecting folks
>>> trying it. I think both.
>>
>>
>> Each PNG chunk is a finite sequence of bytes. Thus, a long enough
>> regex can parse a stream of PNG chunks.
>
>
> Sure, sure.
>
> Oh, don't mind me, I'm just shooting the breeze here. If I sounded too
> negative, it's because I'm a dinosaur in Internet years and I mostly sit
> back and gawk at the younger folks who enthusiastically apply themselves to
> interesting problems such as this one... :-) ;-) It's a generation gap
> thing, no biggie.

A gap of many centuries, in fact, when the burning question
"Can several angels be in the same place?" was hotly debated.