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zevv / npeg

PEGs for Nim, another take
MIT License
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Another concatenation symbol? #3

Closed khchen closed 5 years ago

khchen commented 5 years ago

I like this module very much! Thanks for your effort.

However, when I try to use it in my projects, I found it is hard to read the PEG grammar because that concatenation and matches 0 or more times use the same symbol *.

Is it possible to use another symbol for concatenation, for example: ~, or others?

zevv commented 5 years ago

That's not without problems: because the NPeg grammar is parsed by the Nim compiler, Nim's operator precedence applies. In PEGs, concatenation has precedence over ordered choice, which matches nicely with the Nim * and | operators. (In the original PEG syntax, the symbol for ordered choice is /, but that also has wrong precedence, thus the |) The % operator is not yet used in NPeg and has a higher precedence then |, so theoretically that could replace concatenation, although I'm not sure if that is any better.

I think the only way to get rid of the current notation is to parse PEGs from strings instead of from Nim code; that would allow for any syntax, but has its downsides as well (more complex code, breaks syntax highlighting, and makes Nim code embedded impossible or non-trivial)