This is an ongoing series of build your own X , where I build and understand how various software programs/tools that we use everyday are designed and built.
This is a test spec driven guide to help you build a simple regex engine.
This regex engine supports the following syntax:
| Syntax | Meaning | Example | matches |
|---|---|---|---|
| a | Matches the specified character literal | q | q |
| * | Matches 0 or more of the previous character | a* | "", a, aa, aaa |
| ? | Matches 0 or 1 of the previous character | a? | "", a |
| . | Matches any character literal | . | a, b, c, d, e ... |
| ^ | Matches the start of a string | ^c | c, ca, caa, cbb ... |
| $ | Matches the end of a string | a$ | ba, baaa, qwerta ... |
The goal is to provide a syntax robust enough to match a large portion of regex use cases with minimal code. The included solution is under 40 LOC.
This repo has an accompanying blog post that explains the solution here
npm install
npm testThis project requires a strong understanding of recursion and wonderfully showcases it's elegance with a non-trivial example.
This was possible due to Nicholas Drane's build your own regex