I don't think most languages in widespread use have lexers that are regular. Here the same author gives the example of Python's indentation requiring a stack:

I don't think most languages in widespread use have lexers that are regular. Here the same author gives the example of Python's indentation requiring a stack: http://trevorjim.com/python-is-not-context-free/ http://trevorjim.com/python-is-not-context-free/ Also Haskell: http://trevorjim.com/haskell-is-not-context-free/ http://trevorjim.com/haskell-is-not-context-free/ I'm pretty sure in JavaScript that the /s+/ regex syntax can't be recognized with a regular language. Perl is of course insane -- it's not even statically parseable [1]. Shell isn't context-free. The theme of this set of posts is that most languages used in practice aren't expressible with CFGs, and I agree. I didn't prove it but he shows how you would prove it. [1] http://www.oilshell.org/blog/2016/10/20.html http://www.oilshell.org/blog/2016/10/20.html (see the end of this post for links about C++, Perl, Make)