The 1960s elegance behind Go's regexp

The presentation is given at FOSS Asia Summit 2017

Transcript

1. The 1960s elegance behind Go’s regexp 19 MarchFOSS Asia ‘17 Jalem Raj Rohit
2. What this talk is about? About the two approaches to regex matching. - One used in almost all standard regex interpreters, like Python, Perl, etc - The other one used in some implementations like, awk, grep, sed, etc And Go, of course
3. What exactly are Regular Expressions? - It’s a style of describing character strings - If a string successfully describes a regex, then it is called a match
4. Examples: Let’s say e1 matches “s” and e2 matches “t”: ➔ Alternation If e1 | e2 ⇒ s or it ➔ Concatenation e1 e2 ⇒ st. ➔ e1* 0 or more s ➔ e1+ 1 or more s
5. Perl vs Golang time comparison for matching a?a?a?aaa with respect to the string length
6. Aaaand welcome to: The world of super awesome Computer Science ! and Super awesome algorithms !
7. Meet Finite Automata - It’s also known as State Machines - ← This one is a Deterministic Finite Automata (or a DFA)
8. Also, meet NFA - NFA stands for Nondeterministic Finite Automata - Example on the left - It has multiple legit choices in state S2 Which one to choose? :( - Also, the machine can’t peek ahead
9. Converting Regexes to NFAs - This would be the basic unit of the NFA - Concatenation be like: - Aaaand alternation
10. Perl’s algorithm at work - Also, called the backtracking approach - Time complexity grows exponentially for pathological regex matches, as the string size grows. - Literally, out of the window
11. Can we make this better?
12. Thompson’s algorithm at work - Guesses both options simultaneously - Allows the machine to be in multiple states at the same time - Linear time complexity. Yayyy !!!
13. Again, comparison of the algorithms
14. Again ….
15. Special Shoutout to GopherData - An attempt to bring together Go’s and gophers’ efforts in Data Science and Analytics - Github: https://github.com/gopherdata - Twitter: https://twitter.com/GopherDataIO
16. THANK YOU - Github: Dawny33 - Twitter: @data__wizard (<-- 2 _’s there) - Facebook: rajrohit.33