> I'm curious why BNF was chosen vs EBNF. I'm new to parsers and grammar. Isn't EBNF easier/simpler to write complex rules?
I can't speak to the specific reasons the OP chose, but I can speak to generalities.
Generally speaking, every parser engine out there that supports EBNF supports different extensions of EBNF [+]. They aren't portable from one to another, and that can lock you in. So if you get frustrated with the engine at some point and want to ditch it, it becomes harder to.
BNF does make it harder to write complex rules, but if your goal is a self-hosted compiler, like this one appears to be, you might use BNF for the host compiler, and then choose something more expressive now you can use the language you've built.
There are tradeoffs in everything. BNF tends to be faster, and more portable with more documentation. EBNF handles more complex cases, but you might have to learn one specific tool rather than a standard you can use everywhere.
[+] There is an EBNF standard. However, parser/lexer engines still extend it in their own incompatible ways. ISO tried to standardise it, and just ended up adding to the chaos, and now even they don't recommend their own.
But of course, as shanka commented, it isn't a standard that is followed practically. This is just a demonstration of https://xkcd.com/927/ in real life.
I can't speak to the specific reasons the OP chose, but I can speak to generalities.
Generally speaking, every parser engine out there that supports EBNF supports different extensions of EBNF [+]. They aren't portable from one to another, and that can lock you in. So if you get frustrated with the engine at some point and want to ditch it, it becomes harder to.
BNF does make it harder to write complex rules, but if your goal is a self-hosted compiler, like this one appears to be, you might use BNF for the host compiler, and then choose something more expressive now you can use the language you've built.
There are tradeoffs in everything. BNF tends to be faster, and more portable with more documentation. EBNF handles more complex cases, but you might have to learn one specific tool rather than a standard you can use everywhere.
[+] There is an EBNF standard. However, parser/lexer engines still extend it in their own incompatible ways. ISO tried to standardise it, and just ended up adding to the chaos, and now even they don't recommend their own.