Support Left recursive PEG Grammars

[yhirose]

https://medium.com/@gvanrossum_83706/left-recursive-peg-grammars-65dab3c580e1

[mingodad]

Packcc https://github.com/arithy/packcc has it but it has a high toll on memory usage.

[yhirose]

cpp-peglib supports 'Infix expression by Precedence climbing', and the feature can properly express 'Operator associativity'. But the downside of this approach is that it introduces the special PEG syntax. If the parser supports left recursive PEG grammars, we can specify such operator associativity with the normal PEG syntax.

https://github.com/yhirose/cpp-peglib#parsing-infix-expression-by-precedence-climbing

[mingodad]

Some people say that direct left recursion is easier than indirect left recursion.
I found this links that can help somehow:

• https://github.com/orlandohill/peg-left-recursion
• https://github.com/sacek/LPegLJ
• sacek/LPeg@17bb675