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C4 – C in 4 functions

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Re: C4 – C in 4 functions

#41

Post by PavlovsCat »

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…

Writing software is not a contest, period :) It may be for some, it may be for you, but you don't get to sign up other people for it without their consent.

Re: C4 – C in 4 functions

#42

Post by JoeAltmaier »

sedachv wrote: post #40
JoeAltmaier wrote: post #20

Earlier quoted context omitted.

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.

Bison and Flex work fine - do they count as 'parser generators'?

Re: C4 – C in 4 functions

#43

Post by _wmd »

tehwalrus wrote: post #5
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…

The variable names thing really annoyed me too - a habit of code golf, and people who were originally trained in an old FORTRAN edition that had a 6 or 7 char limit on names.

Unless you're talking about a large piece of software composed entirely of single character functions and variable names, I pretty much disagree. Verbose variable names do not magically teach those reading a piece of code how it works, simultaneously they tend to make it impossible to write many kinds of expressions concisely, and consequently they regularly damage the readability of more complex pieces of code (e.g. arithmetic expressions involving 3 or more terms).

The same goes for symbolic constants. Sometimes (but not exactly "often"), use of numeric literals can vastly improve the maintainability of some code, assuming the reader understands how to maintain it in the first instance.

As for increasing reader comprehension, carefully thought out comments are a better mechanism by far.

In this case, it is sufficient to know that the file is a compiler/interpreter for its entirety to make sense, assuming the reader has implemented (or at least understood the principles behind) a compiler/interpreter in their past. Expanding the function/variable names, splitting "complicated" expressions out into their own functions, etc., does not magically improve the uninitiated's chance of understanding what is going on

Re: C4 – C in 4 functions

#44

Post by TazeTSchnitzel »

stcredzero wrote: post #39
marktangotango wrote: post #25

Earlier quoted context omitted.

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…

Most interpreters (not all, but most) are actually a compiler and a VM, yes. The difference between a "compiler" and an "interpreter", in practise, seems to be that "compilers" lack a built-in interpreter.

Re: C4 – C in 4 functions

#45

Post by tromp »

privong wrote: post #6
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…

> Writing software is not a contest for who can write the most amount of code in the most cryptic way. It can be: http://ioccc.org/

The IOCCC is more about writing the least amount of code in the most cryptic way.

For example, my entry http://www.ioccc.org/2012/tromp/hint.html is a 25 line "BLC in 7 functions".

Similar to C4, but completely unmaintainable, it compiles Binary Lambda Calculus to bytecode which is then interpreted by a virtual machine.

Re: C4 – C in 4 functions

#48

Post by userbinator »

From a cursory glance this appears to be a much-condensed recursive-descent parser with all of the usual parsing functions moved into one, so it's not all that difficult to understand. I think recursive-descent is one of the easiest to intuitively understand parsing algorithms, and it also makes for some concise code; it's also far easier to debug a recursive-descent parser than one of the traditional table-driven ones.

Edit: OTCC (http://www.bellard.org/otcc/ ) is another extremely tiny (to the point of being obfuscated) example of a compiler using a recursive-descent parser.

Re: C4 – C in 4 functions

#49

Post by stcredzero »

TazeTSchnitzel wrote: post #44
stcredzero wrote: post #39

Earlier quoted context omitted.

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…

Most interpreters (not all, but most) are actually a compiler and a VM, yes. The difference between a "compiler" and an "interpreter", in practise, seems to be that "compilers" lack a built-in interpreter.

That's another very good point. One can just as well think of the VisualWorks Smalltalk VM as a compiler (which is actually implemented in Smalltalk) with an interpreter+JIT which also functions as a linker. This means, one can also think of Smalltalk as a compiled language with lots of late binding that makes for a more complicated linker. (JIT) Then the part that's a byte code interpreter can be thought of as an "optimization" on the compiler+linker combination. In fact, if you don't want to bother with flexible debugging, you could implement Smalltalk as a compiled language with "fancy linking" and no interpretation at all.

Any interpreter vs. VM distinction is mostly a social construct. Looked at technically, it's a mishmash.

Re: C4 – C in 4 functions

#50

Post by sehugg »

more_original wrote: post #31
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(bl…

I don't think it supports forward references either, which also makes it more like Pascal.
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