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Well, you can't parse perl without running parts of it. You can't parse lisp without running reader macros. You can't parse TeX without running parts of it.

Well, you can't parse perl without running parts of it. You can't parse lisp without running reader macros. You can't parse TeX without running parts of it. You can't parse C without parsing header files. (Ok, that one is as bit different, because header files are just C code as well).

0x0 13y ago
C++ templates are turing complete, so I guess you can't parse C++ without "running" the templates either. http://stackoverflow.com/questions/189172/c-templates-turing-complete http://stackoverflow.com/questions/189172/c-templates-turing...
- ay 13y ago
  FWIW, the C preprocessor can be used to calculate PI as well: http://chaos-pp.cvs.sourceforge.net/chaos-pp/order-pp/example/bottles.c?revision=1.10&view=markup http://chaos-pp.cvs.sourceforge.net/chaos-pp/order-pp/exampl...
- kivikakk 13y ago
  No. The fact that a feature is Turing complete doesn't make the language unparseable. C is Turing complete, but you don't need to run the program to parse C. Likewise for parsing C++ templates.
  - 0x0 13y ago
    But is parsing C turing-complete? Because that's what I took away from reading about C++ templates - the turing-completeness happens at the parsing/preprocessing stage, before the compiler's code generator even starts translating. Was I wrong? Wouldn't a smart IDE that resolves types (for example for tab completion or type hints), looking at the Factorial<N> thing, have to solve for the value for Factorial<4>?
    - kivikakk 13y ago
      No. (You need parse all includes to know typedefs, but that's it.) C++ is awkward for a different reason, but there's nothing unparseable about it. Resolving types for tab completion/hinting is getting closer to static analysis (at least, with C++ it is), but parsing is well and truly done by that stage. There's nothing about template<4> that can't be parsed, and nothing about the templates or instantiations thereof causes the syntax to be interpreted differently; this is probably the requirement for a parser to be Turing complete. Perl is actually unparseable without execution: you can modify the allowed syntax mid-parse, based on some condition known only at runtime. Nothing about a template argument (for example) in some call causes a later template definition to be interpreted according to different syntax rules.
      - 0x0 13y ago
        Makes perfect sense, and I see they're not the same now. Thanks for the explanation! :)
      - ExpiredLink 13y ago
        > C++ is awkward for a different reason, but there's nothing unparseable about it. Some corner cases in C++ are ambiguous. Those are 'resolved' by guessing what may be more suitable in the current context.
JulianMorrison 13y ago
But you can parse Go without running anything.
- gngeal 13y ago
  You can parse any language without running anything if you do it in your head. But most of us run at least the parser to do that. :-)

0x0 13y ago

C++ templates are turing complete, so I guess you can't parse C++ without "running" the templates either. http://stackoverflow.com/questions/189172/c-templates-turing-complete http://stackoverflow.com/questions/189172/c-templates-turing...

ay 13y ago
FWIW, the C preprocessor can be used to calculate PI as well: http://chaos-pp.cvs.sourceforge.net/chaos-pp/order-pp/example/bottles.c?revision=1.10&view=markup http://chaos-pp.cvs.sourceforge.net/chaos-pp/order-pp/exampl...
kivikakk 13y ago
No. The fact that a feature is Turing complete doesn't make the language unparseable. C is Turing complete, but you don't need to run the program to parse C. Likewise for parsing C++ templates.
- 0x0 13y ago
  But is parsing C turing-complete? Because that's what I took away from reading about C++ templates - the turing-completeness happens at the parsing/preprocessing stage, before the compiler's code generator even starts translating. Was I wrong? Wouldn't a smart IDE that resolves types (for example for tab completion or type hints), looking at the Factorial<N> thing, have to solve for the value for Factorial<4>?
  - kivikakk 13y ago
    No. (You need parse all includes to know typedefs, but that's it.) C++ is awkward for a different reason, but there's nothing unparseable about it. Resolving types for tab completion/hinting is getting closer to static analysis (at least, with C++ it is), but parsing is well and truly done by that stage. There's nothing about template<4> that can't be parsed, and nothing about the templates or instantiations thereof causes the syntax to be interpreted differently; this is probably the requirement for a parser to be Turing complete. Perl is actually unparseable without execution: you can modify the allowed syntax mid-parse, based on some condition known only at runtime. Nothing about a template argument (for example) in some call causes a later template definition to be interpreted according to different syntax rules.
    - 0x0 13y ago
      Makes perfect sense, and I see they're not the same now. Thanks for the explanation! :)
    - ExpiredLink 13y ago
      > C++ is awkward for a different reason, but there's nothing unparseable about it. Some corner cases in C++ are ambiguous. Those are 'resolved' by guessing what may be more suitable in the current context.

JulianMorrison 13y ago

But you can parse Go without running anything.

gngeal 13y ago
You can parse any language without running anything if you do it in your head. But most of us run at least the parser to do that. :-)