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A) Python is not context-free; this is a common misconception: http://trevorjim.com/python-is-not-context-free/ http://trevorjim.com/python-is-not-context-free/

A) Python is not context-free; this is a common misconception: http://trevorjim.com/python-is-not-context-free/ http://trevorjim.com/python-is-not-context-free/ B) No one feature of a grammar provides context-freedom. It's not meaningful to compare Go's grammar to another grammar; it's meaningful to compare Go's grammar as-is to the way it would be if it allowed both forms. In this case, I believe the same-line braces rule is not strictly necessary by itself (they could have gotten a context-free grammar other ways), but this was (part of) one approach.

lucian1900 13y ago
It is context free. Just because two tokens (INDENT, OUTDENT) are different to lex doesn't mean the grammar isn't context free. The only reason same-line braces are required is semicolon insertion. There are other ways to express the grammar of a language without semicolons and remain context-free.
- chimeracoder 13y ago
  > There are other ways to express the grammar of a language without semicolons and remain context-free. Yes, you could use s-expressions, for example. I never said that this was the only way; I just explained part of the reason for the choice.
  - lucian1900 13y ago
    No, there are other ways to express the exact same syntax with a context-free grammar, for example making newlines a significant token.
swift 13y ago
IMO that article doesn't really say anything interesting. There is no clear dividing line between the lexer, the parser, and semantic analysis. You have a great deal of freedom to move work between these phases, and what the grammar you're using at the parser level looks like can change drastically as a result. If Python's lexer is not regular, it doesn't change the fact that the parser uses a context-free grammar over the resulting lexemes. Whether that's the right approach is an engineering tradeoff and nothing more.

lucian1900 13y ago

It is context free. Just because two tokens (INDENT, OUTDENT) are different to lex doesn't mean the grammar isn't context free. The only reason same-line braces are required is semicolon insertion. There are other ways to express the grammar of a language without semicolons and remain context-free.

chimeracoder 13y ago
> There are other ways to express the grammar of a language without semicolons and remain context-free. Yes, you could use s-expressions, for example. I never said that this was the only way; I just explained part of the reason for the choice.
- lucian1900 13y ago
  No, there are other ways to express the exact same syntax with a context-free grammar, for example making newlines a significant token.

swift 13y ago

IMO that article doesn't really say anything interesting. There is no clear dividing line between the lexer, the parser, and semantic analysis. You have a great deal of freedom to move work between these phases, and what the grammar you're using at the parser level looks like can change drastically as a result. If Python's lexer is not regular, it doesn't change the fact that the parser uses a context-free grammar over the resulting lexemes. Whether that's the right approach is an engineering tradeoff and nothing more.