4 ms·

Judging from the comments in c4.cpp, it probably only supports enough of a subset to compile itself. Granted, while building a parser that can parse (let alone

• JoeAltmaier 12y ago
  You can build a C parser in an afternoon. It only has a few language constructs. Declarations are the hardest. Scanners are readily available for expressions and constants.
  • cbhl 12y ago
    I would be worried about handling the not-context-free parts of the language: http://trevorjim.com/c-and-cplusplus-are-not-context-free/ http://trevorjim.com/c-and-cplusplus-are-not-context-free/ How would you handle these?
    • JoeAltmaier 12y ago
      Scanner has to have access to the symbol table, emit 'ident' or 'type' as appropriate. So not a pure context-free parser.
      • sedachv 12y ago
        Yes. This is the reason it is way easier to hand-build a parser for C than try to use any kind of parser generator.
        • JoeAltmaier 12y ago
          Bison and Flex work fine - do they count as 'parser generators'?
          • sedachv 12y ago
            Flex does not work fine, that's why you need the lexer hack: https://en.wikipedia.org/wiki/The_lexer_hack https://en.wikipedia.org/wiki/The_lexer_hack Non-working (no lexer hack) Flex and Bison specification for C99: https://gist.github.com/codebrainz/2933703 https://gist.github.com/codebrainz/2933703 653 lines Hand-written recursive-descent C parser and pre-processor (something not handled by Lex/Yacc) that produces executable Common Lisp code: https://github.com/vsedach/Vacietis/blob/master/compiler/reader.lisp https://github.com/vsedach/Vacietis/blob/master/compiler/rea... 935 lines
            • JoeAltmaier 12y ago
              You can put whatever code you want into the Flex phrase rules. The 'lexer hack' can be implemented there. That's what I do whenever I have to parse something like C.
              • sedachv 12y ago
                Exactly. You have to drop hooks into the lexer from the parser, and by the time you're done you end up with just as much code. Only it's slower than a recursive-descent parser would be, and a lot of the time parsing speed really matters because it shows up as user-visible latency.
                • vidarh 12y ago
                  While I have a strong dislike for lex/yacc and descendants, the "hooks" you need for C are trivial. As far as I remember the only thing you need is an ability for the lexer to check whether or not a given identifier is a variable or type. Even that is only needed if you want to report more specific information up to the parser. E.g. Clang doesn't. In Clang it is instead the parser that looks up the information in order to figure out what type of identifier it has received.
  • rui314 12y ago
    C is not a simple language as a CIL guy says [1]. I wrote my own C compiler [2] and I can say that writing a parser was harder than I thought. It would take more than half a day at least. [1] http://www.cs.berkeley.edu/~necula/cil/cil016.html http://www.cs.berkeley.edu/~necula/cil/cil016.html [2] https://github.com/rui314/8cc https://github.com/rui314/8cc
    • zik 12y ago
      Yes, I also wrote my own C interpreter and the parser was a lot more than a day's work.
    • vidarh 12y ago
      That first link is almost all about language semantics, not parsing issues. As for your example, I'll be solomonic and say that you and Joe are right, of sorts (though I do think it'd be more than an afternoon). It's certainly far more than a days work if you handwrite a lexer and parser that does the amount of additional work that yours do (AST construction; a lot of error reporting and sanity checking). But you can get very far with C very quickly if you use parser generation tools and have prior experience writing compilers and your goal is "just" to get something to parse it as quickly as possible - it's a tiny language. Of course, in practice most real compilers don't use these parser-generation tools exactly because things like proper error reporting etc. is far harder, and a simple recursive descent parser is so much easier to work with.
• verytrivial 12y ago
  Indeed. The lack of a case statement in the run loop is a bit of a giveaway. Excellent work nonetheless.