Comment by layer8
3 hours ago
But that’s not how humans writing code generally think about ambiguous expressions. You can see that by how few precedence rules programmers tend to internalize, and often prefer extra parentheses to make sure that the parser interprets it the way they mean.
I am not talking about operator precedence, that’s a separate thing. Consider the parsing of math expressions, where juxtaposition of terms denotes multiplication unless it can be interpreted as something else. So f(x+2) is function application, whereas 3(x+2) is multiplication. With a PEG, you just write a standard expression grammar with an additional choice at the end for the implicit multiplication. With a conventional parser, this is much more difficult – you have to explicitly list all the different ways that terms could be next to each other without meaning something else.