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0 pointsEtherlord871y ago0 comments

How do you test a regex to be 100% sure it's valid? I don't think it's possible.

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If it's using classical regex, without backtracking or other extensions, a regular expression is isomorphic to a state machine. You can enumerate combinations doing something like this: https://stackoverflow.com/a/1248566

kids these days and their lack of exposure to finite automata

Etherlord87OP1y ago

- Vehicle steering is easy to test.

- How so? I don't think it's possible to test for all cases...

- Well, it's easy, assuming a car on a non-branching track, moving with a constant speed and without any realistic external influences on it, you can simply calculate the distance traveled using the formula s = v/t. Ah, I wish I'd stop running into fools not knowing Newton's first law of motion...

- ??? Are you well?

loamaa1y ago

I understand you want to refute/diminish the parent comment on finite automata, but I think you are providing a straw man argument. The parent comment does provide an interesting, factual statement. I don't believe finite state automata are at all close in complexity to real-world self-driving car systems (or even a portion thereof). Your closing statement is also dismissive and unconstructive.

I believe finite state modeling is used at NASA, A google search brings up a few references (that I'm probably not qualified to speak to), and I also remember hearing/reading a lecture on how they use them to make completely verifiable programs but can't find the exact one at the moment.

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eutropia1y ago

I should have been more clear perhaps: many regexes are capable of being verified with 100% certainty: https://en.m.wikipedia.org/wiki/Thompson%27s_construction

But not all regexes (eg, those using PCRE extensions afaik) are amenable to such a treatment. Those you just tend to hope they work.

fkyoureadthedoc1y ago

True for most things I think

spurgu1y ago

Aren't you asking how to create software without bugs?

Etherlord87OP1y ago

Well regex isn't Turing-complete, so it's not exactly an analysis of a program. You could reason about regex, about tokens, then describe them in a way that satisfies the specification, but theorizing like this is exactly opposite to "simple" - it would be so much harder than just learning regex. So stating that testing regex is simple is just bs. The author later confirms he is a bullshitter by his follow-up...

j / k navigate · click thread line to collapse

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eutropia1y ago

kids these days and their lack of exposure to finite automata

Etherlord87OP1y ago

- Vehicle steering is easy to test.

- How so? I don't think it's possible to test for all cases...

- ??? Are you well?

loamaa1y ago

1 more reply

eutropia1y ago

I should have been more clear perhaps: many regexes are capable of being verified with 100% certainty: https://en.m.wikipedia.org/wiki/Thompson%27s_construction

But not all regexes (eg, those using PCRE extensions afaik) are amenable to such a treatment. Those you just tend to hope they work.

fkyoureadthedoc1y ago

True for most things I think

spurgu1y ago

Aren't you asking how to create software without bugs?

Etherlord87OP1y ago

j / k navigate · click thread line to collapse