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C4 – C in 4 functions

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Re: C4 – C in 4 functions

#31

Post by more_original »

marcofiset wrote: post #4

I honestly think this is ridiculous. Sure, this is an incredible feat, and congrats. But serioulsy, I would be ashamed to publish such unreadable code under my name. What about naming your variables with descriptive names? What about extracting complex conditions into well named function to understand what is going on (thus defeating the purpose of the "4 functions") ? This list could go on forever... Writing softwar…

> I honestly think this is ridiculous. Sure, this is an incredible feat, and congrats.

It's not that bad (or difficult), really. It's a hand-written parser for a subset of C that emits assembly code right away. This is how compilers like Turbo Pascal used to work (see http://www.pcengines.ch/tp3.htm for an explanation of what's happening).

Sure, you could apply cosmetic changes like making "*++e = bla;" into "emit(bla);" and you could move the cases into independent methods (that are used once), but this isn't meant to be a state-of-the art compiler and it won't become one if one applies best practices to it.

Re: C4 – C in 4 functions

#32

Post by whitten »

petercooper wrote: post #3

I just wanted to credit Reddit's /r/tinycode sub-Reddit for this link: http://www.reddit.com/r/tinycode - it's a pretty cool place to discover minimalistic implementations of things.

Thank you for sharing that link to the tinycode Reddit. Did the original poster (for the C in four functions) participate in that sub-reddit ?

Re: C4 – C in 4 functions

#33

Post by kschults »

methyl wrote: post #9

Unfortunately, I cannot compile it on my OSX 10.10... here's what I get: http://pastebin.com/cVvaYFEH EDIT: just make next() function void and it works. EDIT2: still no fortune :( $ ./c4 hello.c [1] 33920 segmentation fault ./c4 hello.c

For now, you need to add both -Wno-return-type and -m32 when compiling.

Re: C4 – C in 4 functions

#34

Post by cbhl »

marcofiset wrote: post #22
cbhl wrote: post #15

Earlier quoted context omitted.

I actually found the code surprisingly easy to read; "tk" stands for "token", "ty" for "type", and so forth. It's worth noting that compilers don't pop out of thin air -- you have to start with something simple in order to compile a more complicated compiler. Bootstrapping your own self-hosting compiler is a useful academic exercise, and you should try it sometime if you haven't already: http://en.wikipedia.org/wiki/…

Well, if this particular compiler is defined in 4 functions, why couldn't it be made out of more functions, enhancing the readability and maintainability of the code?

There is no reason why couldn't it be made out of more functions. Absolutely none. In fact, you can fork the repository and do the refactoring yourself, right now.

If I had to guess, the functions are tied pretty closely to how the author is parsing the file; "next" (next token), "expr" (expression), "stmt" (statement), and "main".

As for the project being called "C in 4 functions"; at best, I'd argue that's just a linkbait-y title since it's not actually C (it's a subset). I don't have a problem with the code _per se_; just the title.

Re: C4 – C in 4 functions

#35

Post by karlgrz »

marcofiset wrote: post #4

I honestly think this is ridiculous. Sure, this is an incredible feat, and congrats. But serioulsy, I would be ashamed to publish such unreadable code under my name. What about naming your variables with descriptive names? What about extracting complex conditions into well named function to understand what is going on (thus defeating the purpose of the "4 functions") ? This list could go on forever... Writing softwar…

I honestly think this comment is ridiculous. Sure, this is an incredible feat, and congrats. But seriously, I would be ashamed to publish such unreadable English under my name. What about spelling all the words correctly? What about not being an asshole and criticizing someone just because? This list could go on forever... Writing comments is not a contest for who can write the most amount of bullshit in the most non-constructive way.

Re: C4 – C in 4 functions

#36

Post by [deleted] »

whitten wrote: post #32
petercooper wrote: post #3

I just wanted to credit Reddit's /r/tinycode sub-Reddit for this link: http://www.reddit.com/r/tinycode - it's a pretty cool place to discover minimalistic implementations of things.

Thank you for sharing that link to the tinycode Reddit. Did the original poster (for the C in four functions) participate in that sub-reddit ?

[deleted]

Re: C4 – C in 4 functions

#37

Post by pmh »

whitten wrote: post #32
petercooper wrote: post #3

I just wanted to credit Reddit's /r/tinycode sub-Reddit for this link: http://www.reddit.com/r/tinycode - it's a pretty cool place to discover minimalistic implementations of things.

Thank you for sharing that link to the tinycode Reddit. Did the original poster (for the C in four functions) participate in that sub-reddit ?

It would appear so. https://www.reddit.com/r/tinycode/comments/2la785/c4_a_c_com... is the post from /r/tinycode and its OP[0] is the same as the github user[1] for c4.

[0]https://www.reddit.com/user/rswier

[1]https://github.com/rswier

Re: C4 – C in 4 functions

#38

Post by ackalker »

methyl wrote: post #9

Unfortunately, I cannot compile it on my OSX 10.10... here's what I get: http://pastebin.com/cVvaYFEH EDIT: just make next() function void and it works. EDIT2: still no fortune :( $ ./c4 hello.c [1] 33920 segmentation fault ./c4 hello.c

Please try kbrock's fork at https://github.com/kbrock/c4 Check out his 'longs' branch.

Re: C4 – C in 4 functions

#39

Post by stcredzero »

marktangotango wrote: post #25
0x0 wrote: post #18

Would you call this a compiler, an interpreter, a virtual machine, a scripting engine, or a combination of those?

It compiles a c subset to byte code, then executes in a virtual machine. I think generally an intepreter can refer to either a byte code interpreter (ie virtual machine) or an AST walking interpreter. I didn't see a way to embed c4 into a host language, so maybe not a scripting language? IMO the real value of exhibits like this are boiling the problem (lexing, parsing, compiler, interpreting) down to their most basic…

I think generally an intepreter can refer to either a byte code interpreter (ie virtual machine) or an AST walking interpreter.

This brings to mind how fuzzy "interpreter" is as terminology. What is a virtual machine that JIT compiles the byte code or the AST? Is it a JIT implementation of an interpreter? What of implementations that only JIT the most frequently used functions? Wouldn't those be half interpreter and half virtual machine?

When it comes down to it, they're all really virtual machines. The real distinction is how we've come to think of different implementations and the representations sub-culturally. For some reason, it makes us feel better when we call certain things interpreters, because of some meaningless (and sometimes factually challenged) competitive instincts concerning implementation speed. (Also, we arbitrarily feel that byte code is somehow more "machine-y" than an AST.)

So do I have a problem with "interpreter"? Only when people correct others, as if they're making a correction about something fundamental and factual. In reality, the distinction is between machines that are intended to have the same runtime semantics and really the distinction is only around what optimizations are present in their implementations. Furthermore, if you look at those optimizations in detail, the distinction gets even hazier.

Re: C4 – C in 4 functions

#40

Post by sedachv »

JoeAltmaier wrote: post #20
cbhl wrote: post #17

Earlier quoted context omitted.

I would be worried about handling the not-context-free parts of the language: http://trevorjim.com/c-and-cplusplus-are-not-context-free/ How would you handle these?

Scanner has to have access to the symbol table, emit 'ident' or 'type' as appropriate. So not a pure context-free parser.

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.
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