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I want to write a library that is dynamically loadable and callable from C code, but I really don't want to write it in C - the code is security critical, so I want a language that makes it easier to have confidence that my code is correct. What are my options?
To be more specific, I want C programmers to be able to #include this, and -l that, and start using my library just as if I had written it in C. I'd like programmers in other languages to be able to use their favourite tools for linking to C libraries to link to it. Ideally I'd like that to be possible on every platform that supports C, but I'll settle for Linux, Windows and MacOS.
Anything that compiles to native code. So you might Google for that - "languages that compile to native code." See, e.g., Programming languages that compile to native code and have the batteries included
C++ is often the choice for this. Compiles to native code and provided you keep your interfaces simple, easy to write an adapter layer.
Objective C and Fortran are also possible.
It sounds like you are looking for a language with ABI compatibility or which can be described as resulting in native code. So long as it can be compiled to a valid object file (typically an .obj or .o file) which is accepted by the linker, that should be the main criteria. You also then want to write a header file as a convenience for any client code which is written in C (or a closely related language/variant thereof).
As mentioned by others, you need a pretty good reason for choosing a language other than C as it is the lingua-franco of low-level/systems software. Assembler is an option, although harder to port between platforms. D is a more portable - but less widespread - alternative which is designed to produce secure, efficient native code with a minimum of fuss. There are many others.
Almost every security critical application I know of is written in C. I don't believe that there are any other language that has higher real status in producing secure applications.
C is being said to be a poor language for security by people who don't understand.
If you want C programmers to use your library, use C. Doing anything else is tying one hand behind your back whilst trying to walk on a balance beam (the gymnastics equipment). Sure, there are dozens of other languages that are CAPABLE of interfacing to C, but it typically involves using a C layer and then stuffing the C data types into a language specific data type (Java Objects, Python Objects, etc, etc), and when the call is finished, you use the same conversion back to a C data type. Just makes it harder to work with, and potentially slower if you don't get all the design decisions right. And people won't understand the source code, so won't like to use it (see more about this below).
If you want security, then write very good code, wearing your "security aspects" hat firmly on at all times, find a security mailing list or website and post it there for review, take the review comments on board, understand the comments, and fix any comments that are meaningful to fix. Distribute the source code to the users, so people can see what your code does. Those that understand security will know what to look for and understand that you have done a good job (or a bad job, whichever is applicable) - and those who don't will hopefully trust the right pople. If it's good, people will use it. If it's "hidden", and not easy to access, you won't get many customers, no matter what language you use.
Don't worry, you won't reveal anything more from releasing source. If there is a flaw in the code, and it is popular (or important) enough, someone will find the flaw, even if you publish only binaries. For those skilled in reverse engineering, not having source code is only a small obstacle.
Security doesn't stem from using a specific language or a specific tool, it stems from good design and good basic understanding of the problems with security.
And remember security by obscurity (whether that means "hidden source code" or "unusual language" or something else obscure) is false security.
You might be interested in ATS, http://ats-lang.sourceforge.net/. ATS compiles via C, can be as efficient as C, and can be used in a way that is ABI-compatible with C. From the project website:
ATS is a statically typed programming language that unifies implementation with formal specification. It is equipped with a highly expressive type system rooted in the framework Applied Type System, which gives the language its name. In particular, both dependent types and linear types are available in ATS. The current implementation of ATS (ATS/Anairiats) is written in ATS itself. It can be as efficient as C/C++ (see The Computer Language Benchmarks Game for concrete evidence) and supports a variety of programming paradigms
ATS's dependent and linear type system helps produce static guarantees about your code, including various aspects of resource management safety.
Chris Double has been writing a series of articles exploring the power of ATS's type system for systems programming here: http://bluishcoder.co.nz/tags/ats/. Of particular note is this article: http://bluishcoder.co.nz/2012/08/30/safer-handling-of-c-memory-in-ats.html
This document covers aspects of calling back and forth between ATS and C code: https://docs.google.com/document/d/1W6DYQApEqKgyBzMbvpCI87DBfLdNAQ3E60u1hUiMoU0
The main downside is that dependently-typed programming is still a daunting prospect, even for non-systems programming. The syntax of the language is also a bit weird: consider lexical quirks such as the use of abst#ype as a keyword. Finally, ATS is to some degree a research project, and I personally don't know whether it would be sensible to adopt for a commercial endeavour.
Theoretically, it's going to be Fortran: less indirection (as in: my array is [here], not just a pointer to here, and this is true of most but not all of your data structures and variables).
However... There are many gotchas and quirks in Fortran: not, perhaps, as many as in C but you probably know your way around C rather better than Fortran. Which is the point behind most of the comments saying 'Know your code' - but do you really know what your compiler is doing?
Knowing you, I'm prepared to take it on trust that you do, for C. Most programers don't. You do not know and cannot know what a local JVM or JIT compiler does, and that's a black hole in your security model if you're using Java or C# r scripting languages.
Ignore anyone who tells you that the hairy-chested he-men of secure computing write their own assembler: they probably don't even know the security errors they're making in any and all nontrivial projects they release. Know your compiler, indeed.
You could write it in lua - providing a C API to a Lua library is relatively straight forward. C++ is also an option, though of course you'd have to write C wrappers and make sure no exceptions can escape your functions. But honestly, if it's security critical the minor inconveniences of the C language shouldn't be that much of a big deal. What you really should be doing is prove the correctness of your program where feasible, and test extensively where it's not.
You can write a library in Java. JNI is normally used to call C from Java, but it can be used the other way around.
There is finally a decent answer to this question: Rust.
I'm looking for a higher-level system language, if possible, suitable for formal verification, that compiles to standard C, so that it can be run cross-platform with (relatively) low overhead.
The two most promising such languages I've stumbled during the past few days are:
BitC - While the design goals of this language match my needs (it even supports the functional paradigm), it is in very unstable state, the documentation is out of date, and, generally, it seems like a very long shot for a real-world project.
Lisaac - It supports Design-by-contract, which is very cool and has a relatively low performance overhead. However the website is dead, there hasn't been a new release since '08 and generally it seems the language is dead.
I'd also like to note that it's not meant for a real-time system, so a GC or, generally, non-determinism (in the real-time sense), is not an issue.
The project involves mainly audio processing, though it has to be cross-platform.
I assume someone would point me to the obvious answer - "plain ol' C". While it is truly cross-platform and very effective, the code quantity would probably be greater.
EDIT: I should clarify that I mean cross-platform AND cross-architecture. That is why I consider only languages, compiled to C in the first place, but if you can point me to another example, I'd be grateful :)
I think you may become interested in ATS. It compiles to C (actually it expresses and explains many C idioms and patterns from a formal type-theoretic perspective, it has even been proposed to prepare a book of sorts to show this -- if only we had more time...).
The project involves mainly audio processing, though it has to be cross-platform.
I don't know much about audio processing, I've been mainly doing some computer graphics stuff (mostly the basic things, just to try it out).
Also, I am not sure if ATS works on Windows (never tried that).
(Disclaimer: I've been working with ATS for some time. It is bulky and large language, and sometimes hard to use, but I very much liked the quality of programs I've been able to produce with it, for instance, see TEST subdirectory in GLES2 bindings for some realistic programs)
The following doesn't strictly adhere to the requirements but I'd like to mention it anyway and it is too long for a comment:
Pypy's RPython can be translated to C. Here's a nice talk about it. It's been used to implement Smalltalk, JavaScript, Io, Scheme, Gameboy (with various degree of completeness), but you can write standalone programs in it. It is known mainly for its implementation of Python language that runs on Intel x86 (IA-32) and x86_64 platforms.
The translation process requires a capable C compiler. The toolchain provides means to infer various things about the code (used by the translation process itself) that you might repurpose for formal verification.
If you know both Python and C you could use cython that translates Python-like syntax to C. It is used to write CPython extensions.
I've been learning C: it's a beautiful, well-thought-out language. However, it is so low-level that writing any sort of major project becomes tedious.
What higher-level language has the most C-like syntax—but without all the clutter that you find in something like C++. Does one exist?
What higher-level language has the most C-like syntax—but without all the clutter that you find in something like C++?
I'm going to answer a slightly different question:
What is a language that is like C in that it is well designed and beautifully thought out, is like C in that it is good for systems programming, allows people to program at a higher level than C, and is relatively uncluttered?
I don't think this question has a single right answer, but here are three worthy candidates (in alphabetical order):
D. The D language is designed essentially as a better, cleaner C++. Like C++, D is explicitly designed to incorporate a lot of features, but one hopes in a cleaner, more harmonious way than C++. A major difference that enables programmers to work at a higher level is that memory is managed automatically by the language and safety is guaranteed by the compiler (and run-time system) through garbage collection.
Go. Go scores very high on being well designed and beautifully thought out: Rob Pike is a master designer and has been practicing this particular craft for 25 years. Its explicit goal is to be uncluttered and to make systems programming "fun again". Go is still a new language, and Rob has learned much from Squeak, Newsqueak, Alef, and Limbo. Because Rob understands that a great design is one with no unnecessary parts, Go is clean and uncluttered. Its primary features that are higher-level than C are type safety, garbage collection, and an excellent concurrency model.
Java. Java has a well-designed core (see Jim Waldo's book Java: The Good Parts) but unfortunately suffers from the clutter that any mature, successful language accumulates. The features of Java that make it most suitable for higher-level programming are interfaces, garbage collection, and exceptions.
The common thread here is using garbage collection to relieve the programmer of the burden of memory management. This is a major boost to productivity.
Each of these languages has much to recommend it. My own taste is for languages that are small and simple, and I admire Rob Pike's body of work very highly, so if I had to pick one for myself, it would be Go, despite the fact that it is new and unproven.
In C++ you can write C code and have it compile successfully as C++ (mostly). Therefore, although I suggest that your term "clutter" is both derogatory and ambiguous, the only clutter you will have is what you choose to write yourself. You can use C++ as a bigger tool-bag without using all the tools (or clutter if you prefer).
The answer therefore is C++ whether you like it or not. Most other C-like languages add OO features, which is perhaps what you regard as clutter, but you do not get something for nothing and you need to have syntax to support the additional features. Such languages include:
Java
C#
Objective-C
D
Of these Objective-C is probably the most C-Like since it is a superset of C in the way that C++ is not quite. It is also the preferred language for OSX and iPhone/iPod Touch development, which may be attractive.
Java is ubiquitous but probably best described as superficially C-like. C# has limited cross-platform support but is the path of least resistance for Windows GUI development with excellent free development tools. C# also has a simpler but more restrictive OO implementation than C++ so may meet your requirements, but its resemblance to C/C++ can be misleading; it is fundamentally different in how it works in a similar manner to Java. D is somewhat of a niche, being developed by a single author (albeit the author of the once renowned Zortech/Symantec C++ compiler).
Regarding it being "low level" and "tedious", when embarking on a "major project", you would seldom start from scratch with only the standard library and OS API available, you would make use of third-party and in-house developed libraries to quickly develop higher level functionality. That said, an OO approach is generally much more amenable to this 'code-reuse' approach, and of course C++'s standard library and third-party libraries are more extensive (not least because it can use C libraries as well as C++ libraries). In fact I would suggest that apart form support for OO, the only thing that makes C++ higher-level is its extensibility via classes as first-class objects. It remains suitable as a systems-level language nonetheless.
Google's Go language has a similar syntax (though different enough I suppose) and semantics, though with garbage collection, polymorphism, etc., built into the language.
The D programming language is an attempt to be what C++ should have been (not bashing on C++ at all it is my primary language) and I quote from the website, "D is a systems programming language. Its focus is on combining the power and high performance of C and C++ with the programmer productivity of modern languages like Ruby and Python. Special attention is given to the needs of quality assurance, documentation, management, portability and reliability. " The issue with D is it is relatively new compared to a lot of languages but luckily it can still use C libraries which allows it to access a large pre-existing code base. Certainly worth checking out.
Java is another option however it is notably slower than C. Syntactically it is very similar and offers a nice object orientated environment for writing code. It is also considered by most to be a safer language than C and C++. It is widely used in enterprise.
Python while syntactically not like C is a high level Object Orientated Programming Language that is very popular and can import C modules which may be very useful down the track.
This is too broad a question and is best made Community wiki.
However, in my mind, the main distinguishing feature of C is it's compactness. The whole language can be described in a small book like K&R. One can remember all the syntactic details without much effort (since there are so few of them) and it doesn't try to protect it's users from themselves.
Languages like C++ are much more baroque. It's quite hard to remember all the rules and exceptions. I feel the same way about Perl and Ruby. There are lots of things to remember and lots of things to watch out for.
I feel the same sense of compactness with Python (although perhaps not as much as C). There's very little "special syntax" and all libraries and modules are operated upon in a similar fashion.
This (probably like most other comments on this question) is a personal evaluation and is by no means a final word.
Probably Java and C#... Java a little more so I think.
And it's not the language - it's all about the libraries. Try out Qt (http://qt.nokia.com/). It's for C++ and I know you said C but I'm just making a point that you'll find yourself writing just as little (and perhaps even less!) code than you'd write for applications in Java or C#. Plus they're native and cross-platform.
All about the libraries.
I've been learning C: it's a beautiful, well-thought-out language. However, it is so low-level that writing any sort of major project becomes tedious.
Some people would say that the second sentence proves that the assertion of the first sentence is false.
Another point is that this is pretty much unanswerable. What is a "high level" language? what are your criteria for "closeness"? Syntax, computational model, performance? And what kind of applications are you wanting to build with this hypothetical language?
And if you just want to confine yourself to languages that "look like" C, why? As someone who has lost count of the number of programming languages he has used, I can tell you that differences in programming language syntax are generally pretty unimportant. You can get used to pretty much any syntax, given time.
This comparison of basic instructions gives you a good idea of what languages are similar to each other.
I would say PHP is most like C except for the $variables, if you can distinguish php the language from php the platform. Java tries in some ways, but is too strongly object oriented to be similar to C.
Javascript has a reasonably C-like syntax, and it's a very popular language. Javascript has a lot of quirks, but it has one powerful similarity to C - it's simple. The complete Javascript specification is very short, and the language is very powerful and high-level. It would be great to clean it up from some of its ugly cruft, though.
I'll just point out that Pascal is semantically (though not so much syntactically) very similar to C, so there are options like Object Pascal, Modula 2, Ada and Oberon out there where you will be re-using most of the non-trivial part of what you already know, the trivial part being the spelling.
You're probably better off sticking with C# or Java in terms of job prospects, though.
EDIT
I'll also add that on the clutter issue, it is important to sort out which clutter is important. C has less "clutter" in it's language definition, true, but the relevant clutter is in source code. Consider the following...
// C
struct mystruct *myvar;
myvar = (struct mystruct *) malloc (sizeof (struct mystruct));
myvar->a = 1;
myvar->b = 2;
myvar->c = 3;
call_something (myvar);
free (myvar);
// C++
auto_ptr<mystruct> myvar (new myclass (1, 2, 3));
call_something (myvar);
The point is that the "clutter" in the language definition is there for a reason. With a little up-front work when writing libraries, a lot of work (and clutter) is avoided down the line. And even when you're writing a library, you benefit from the up-front work done by other library writers.
I'd vote C#. I don't know what you mean by "clutter," but from a usability standpoint, C# is nice because it avoids some of the tedious things of C++, like having to essentially "declare" each of your class's methods twice (prototyping it in the header file, then essentially duplicating the same thing in your class's implementation). Ditching header files was nice in other ways too, like doing away with dependency conflicts in big projects or avoiding circular references. In C#, the compiler takes care of all that (although you still have to set references to other files or assemblies).
I've been doing C# for 10 years and I still miss pointers, which believe it or not, in my opinion, actually made debugging easier!
If you're going to be programming often, it's good to know languages that are explicitly not like each other. It's especially useful to know high level scripting languages like python or ruby. If you can think like a programmer in C you should be fine learning either of these two.
Many big projects take advantage of the rapid prototyping of higher level languages like python or ruby, but also take advantage of low overhead (fast) compiled languages like C/C++.
If you think that C++ is cluttered, then you just don't know how to write effective C++, because nobody forces you to use any of the advanced tools available. You could write a C++ program entirely in C plus your favourite C++ feature (like the AWESOME standard library). That's the definition of uncluttered. A cluttered language would be Java/C#, where you HAVE to put every function in a class. That's clutter.
How about ActionScript 3? It's a lot like Java.
I came across this: Writing a compiler using Turbo Pascal
I am curious if there are any tutorials or references explaining how to go about creating a simple C compiler. I mean, it is enough if it gets me to the level of making it understand arithmetic operations. I became really curious after reading this article by Ken Thompson. The idea of writing something that understands itself seems exciting.
Why did I put up this question instead of asking Google? I tried Google and the Pascal one was the first link. The rest did no seem relevant and added to that... I am not a CS major (so I still need to learn what all those tools like yacc do) and I want to learn this by doing and am hoping people with more experience are always better at these things than Google. I want to read some article written in the same spirit as the one I listed above but that which highlights at least the bootstrapping phases of building a simple C compiler.
Also, I don't know the best way to learn. Do I start off building a C compiler in C or some other language? Do I write a C compiler or some other language? I feel questions like this are better answered once I have some direction to explore. Any suggestions?
Any suggestions?
A compiler consists of three pieces:
A parser
An abstract syntax tree (AST)
An assembly code generator
There are lots of nice parser generators that start with language grammars. Maybe ANTLR would be a good place for you to start. If you want to stick to C roots, try lex/yacc or bison.
There are grammars for C, but I think C in its entirety is complex. You'd do well to start off with a subset of the language and work your way up.
Once you have an AST, you use it to generate the machine code that you'll run.
It's doable, but not trivial.
I'd also check Amazon for books about writing compilers. The Dragon Book is the classic, but there are more modern ones available.
UPDATE: There have been similar questions on Stack overflow, like this one. Check out those resources as well.
I advise you this tutorial:
LLVM tutorial
It is a small example on how to implement a "small language" compiler. The source code is very small and is explained step by step.
There is also the C front end library for the LLVM (Low Level Virtual Machine which represent the internal structure of a program) library:
Clang
For what it's worth, the Tiny C Compiler is a pretty full-featured C compiler in a relatively small source package. You might benefit from studying that source, as it's probably significantly easier to understand than trying to comprehend all of GCC's source base, for instance.
This is my opinion (and conjecture) it will be hard to write a compiler without understanding data structures normally covered in undergraduate (post secondary) Computer Science classes. This doesn't mean you cannot, but you will need to know essential data structures such as linked lists, and trees.
Rather than writing a full or standards compliant C language compiler (at least in the start), I would suggest limiting yourself to a basic subset of the language, such as common operators, integer only support, and basic functions and pointers. One classic example of this was Ron Cain's Small-C, made popular by a series of articles written in Dr. Dobbs Journal in I believe the 1980s. They publish a CD with the James Hendrix's out-of-print book, A Small-C Compiler.
What I would suggest is following Crenshaw's tutorial, but write it for a C-like language compiler, and whatever CPU target (Crenshaw targets the Motorola 68000 CPU) you wish to target. In order to do this, you will need to know basic assembly of which ever target you want to run the compiled programs on. This could include a emulator for a 68000, or MIPS which are arguably nicer assembly instruction sets than the venerable CISC instruction set of the Intel x86 (16/32-bit).
There are many potential books that can be used as starting points for learning compiler / translator theory (and practice). Read the comp.compilers FAQ, and reviews at various online book sellers. Most introductory books are written as textbooks for sophomore to senior level undergraduate Computer Science classes, so they can be slow reading without a CS background. One older book that might be more introductory, but easier to read than "The Dragon Book" is Introduction to Compiler Construction by Thomas Parsons. It is older, so you should be able to find an used copy from your choice of online book sellers at a reasonable price.
So I'd say, try starting with Jack Crenshaw's Let's Build a Compiler tutorial, write your own, following his examples as a guide, and build the basics of a simple compiler. Once you have that working, you can better decide where you wish to take it from that point.
Added:
In regards to the bootstrapping process. Since there are existing C compilers freely available, you do not need to worry about bootstrapping. Write your compiler with separate, existing tools (GCC, Visual C++ Express, Mingw / djgpp, tcc), and you can worry about self-compiling your project at a much later stage. I was surprised by this part of the question until I realized you were brought to the idea of writing your own compiler by reading Ken Thomas' ACM Turing award speech, Reflections on Trusting Trust, which does go into the compiler bootstrapping process. It's a moderated advanced topic, and is also simply a lot of hassle as well. I find even bootstrapping the GCC C compiler under older Unix systems (Digital OSF/1 on the 64-bit Alpha) that included a C compiler a slow and time consuming, error prone process.
The other sort-of question was what a compiler tool like Yacc actually does. Yacc (Yet Another Compiler Compiler or Bison from GNU) is a tool designed to make writing a compiler (or translator) parser easier. Based on the formal grammar for your target language that you input to yacc, it generates a parser, which is one portion of a compiler's overall design. Next is Lex (or flex from GNU) which used to generate a lexical analyzer or scanner, which is often used in combination with the yacc generated parser to form the skeleton of the front-end of a compiler. These tools make writer a front end arguably easier than writing an lexical analyzer and parser yourself. Crenshaw's tutorial does not use these tools, and you don't need to either, many compiler writers don't always use them. Of course Crenshaw admits the tutorial's parser is quite basic.
Crenshaw's tutorial also skips generating an AST (abstract syntax tree), which simplifies but also limits the tutorial compiler. It lacks most if not all optimization, and is very tied to the specific programming language and the particular assembly language emitted by the "back-end" of the compiler. Normally the AST is a middle piece where some optimization can be performed, and serves to de-couple the compiler front-end and back-end in design. For a beginner without a Computer Science background, I'd suggest not worrying about not having an AST for your first compiler (or at least the first version of it). I think keeping it small and simple will help you finish writing a compiler, in its first version, and you can decide from there how you want to proceed then.
You might be interested in the book/course The Elements of Computing Systems:Building a Modern Computer from First Principles.
Note that this isn't about building a "pc" from stuff you bought off newegg. It begins with a description of Boolean logic fundamentals, and builds a virtual computer from the lowest levels of abstraction to progressively higher levels of abstraction. The course materials are all online, and the book itself is fairly inexpensive from Amazon.
In the course, in addition to "building the hardware", you'll also implement an assembler, virtual machine, compiler, and rudimentary OS, in a step-wise fashion. I think this would give you enough of a background to delve deeper into the subject area with some of the more commonly recommended resources listed in the other answers.
In The Unix Programming Environment, Kernighan and Pike walk through 5 iterations of making a calculator working from simple C based lexical analysis and immediate execution to yacc/lex parsing and code generation for an abstract machine. Because they write so wonderfully I can't suggest smoother introduction. It is certainly smaller than C, but that is likely to your advantage.
How do I [start writing] a simple C compiler?
There's nothing simple about compiling C. The best simple C compiler is lcc by Chris Fraser and David Hanson. They spent 10 years working on the design to make it as simple as they possibly could, while still generating reasonably good code. If you have access to a university library, you should be able to get their book.
Do I start off building a C compiler in C or some other language?
Some other language. One time I got to ask Hanson what lessons he and Fraser had learned by spending 10 years on the lcc project. The main thing Hanson said was
C is a lousy language to write a compiler in.
You're better off using Haskell or some dialect of ML. Both languages offer functions over algebraic data types, which is a perfect match to the problems faced by the compiler writer. If you still want to pursue C, you could start with George Necula's CIL, which is a big chunk of a C compiler written in ML.
I want to read some article written in the same spirit as the one I listed above but that which highlights at least the bootstrapping phases...
You won't find another article like Ken's. But Andrew Appel has written a nice article called Axiomatic Bootstrapping: A Guide for Compiler Hackers I couldn't find a free version but many people have access to the ACM Digital Library.
Any suggestions?
If you want to write a compiler,
Use Haskell or ML as your implementation language.
For your first compiler, pick a very simple language like Oberon or like P0 from Niklaus Wirth's book Algorithms + Data Structures = Programs. Wirth is famous for designing languages that are easy to compile.
You can write a C compiler for your second compiler.
A compiler is a complex subject matter that covers aspects of
Input processing involving Lexing, Parsing
Building a symbol store of every variable used such as an Abstract Syntax Tree (AST)
From the AST tree, transpose and build a machine code binary based on the syntax
This is by no means exhaustive as it is an abstract bird's eye view from the top of a mountain, it boils down to getting the syntax notation correct and ensuring that malformed inputs do not throw it off, in fact a good input processing should never fall on its knees no matter how malformed, terrible, abused cases of input that gets thrown at it. And, also in deciding and knowing what output is going to be, is it in machine code, which would imply you may have to get to know the processor instructions intimately...including memory addressing for variables and so on...
Here are some links for you to get started:
There was a Jack Crenshaw's port of his code for C....(I recall downloading it months ago...)
Here's a link to a similar question here on SO.
Also, here's another small compiler tutorial for Basic to x86 assembler compiler.
Tiny C Compiler
Hendrix's Small C Compiler found here.
It might be worthwhile to learn about functional programming, too. Functional languages are well-suited to writing a compiler both in and for. My school's intro compilers class contained an intro to functional languages and the assignments were all in OCaml.
Funny you should ask this today, since just a couple days ago I wrote a lambda calculus interpreter. Lambda calculus is the granddaddy of all functional languages. It's just 200 lines long (in C++, incl. error reporting, some pretty printing, some unicode) and has a two-phase structure, with an intermediate format that could be used to generate code.
Not only is starting small and building up the most practical approach to compilers, it also encourages good, modular, organizational practice.
A compiler is a very large project, although I suppose it wouldn't hurt to try.
I know of at least one C compiler written in Pascal, so it's not the most insane thing you could do. I personally would pick a more modern language in which to implement my C compiler project, both for the simplicity (it's easy to d/l packages for Python, Ruby, C, C++ or Java) and because it will look better on your resume.
In order to do a compiler as a beginner project, though, you will need to drink all of the Agile kool-aid.
Always have something running, even if it doesn't do much of anything. Add things to your compiler only in small steps. ("Frequent releases".) Pick a viciously tiny subset of the language and implement that first. (Support only i = 0; at first and expand things from there.)
If you want a mind-blowing experience that teaches you how to write compilers that compile themselves, you need to read this paper from 1964.
META II a syntax-oriented compiler writing language by Val Schorre.
In 10 pages, it tells you how to write compilers, how to write meta compilers, provides a virtual metacompiler instruction set, and a sample compiler built with the metacompiler.
I learned how to write compilers from this paper back in the late 60s, and used the ideas to construct C-like langauges for several minicomputers and microprocessors.
If the paper is too much by itself (it isn't!) there's an online tutorial which will walk you through the whole thing.
And if getting the paper from the original link is awkward because you are not an ACM member, you'll find that the tutorial contains all the details anyway. (IMHO, for the price, the paper itself is waaaaay worth it).
10 pages!
I would not recommend starting with C as the language to implement, nor with any of the compiler-generator or parser-generator tools. C is a very tricky language, and it's probably a better idea to just make up a language of your own. It can be a little C-like (e.g. use curly backets if you want to indicate the function body, use the same type names, so you don't have to remember what you called everything).
The tools for making compilers and parsers are great, but have the problem of really being a shorthand notation. If you don't know how to create a compiler in longhand, the shorthand will seem cryptic, needlessly restrictive etc. So write your own simple compiler first, then continue on from there. I also recommend you don't start generating actual machine code unless you eat and breathe assembler. Create your own bytecode interpreter with a VM.
As to what language you should use to create your first compiler: It doesn't really matter, as long as the language is fairly complete. You will be reading input text, building data structures from them and writing out binary data. So if a language makes those things easier in any way, that's a point in favor of it. Pick a language you know well, so you can focus on creating the compiler, not learning the language. I usually use an OO language, which makes the syntax tree easier to write, a functional language would probably also work if you are familiar with that.
I've blogged a lot about programming languages, so you might find some useful postings here: http://orangejuiceliberationfront.com/category/language-design/
In particular, http://orangejuiceliberationfront.com/how-to-write-a-compiler/ is a starter on the particulars of parsing common constructs and generating something useful from that, as well as http://orangejuiceliberationfront.com/generating-machine-code-at-runtime/ which talks about actually spitting out Intel instructions that do something.
Oh, regarding bootstrapping of a compiler: You probably won't be able to do that right from the start. There is a fair amount of work involved in creating a compiler. So not only would writing a bootstrapping compiler involve writing the compiler (in some other language), once you have it, you would then have to write a second version of the compiler using itself. That's twice the work, plus the debugging needed in the existing and the bootstrapped new compiler until it all works. That said, once you have a working compiler, it is a good way to test its completeness. OK, maybe not twice the work, but more work. I'd go for the easy successes first, then move on from there.
In any event, have fun!
I've been working on a C program which does quite a lot of string manipulation, and very often needs to be tweaked and recompiled for some sort of special case processing. I've been thinking that embedding some scripting language with good string manipulation support might make sense for the project.
What language would provide the best string manipulation support while being easy to embed in a C program?
For some extra background...
Performance is pretty important (especially startup time)
Needs easily be compiled on multiple platforms (Linux, Solaris, Win32 (ideally with MinGW), Darwin)
Needs to be a language which will still be around in 5 years time
I've looked a little at Python (perhaps too heavy weight?) and Lua (perhaps not focused on string manipulation?) but don't really know enough about them or what other choices might be out there.
I've never regretted using Lua.
It's very easy to embed in your application. In fact, now I usually don't write C applications, i just write C libraries and control them from Lua.
Text manipulation isn't its best feature, but it's certainly far better than C alone. And the LPEG library makes building parsers almost trivially easy, putting any regex to shame (but still has a couple of regex-like syntaxes if you prefer them).
Lua stands head and shoulders above other choices.
... best string manipulation support while being easy to embed?
Lua is designed to be embedded in C; the API is clear and easy to use; the documentation is terrific.
Some other responses have denigrated Lua's string capabilities. I think they're underestimating Lua.
Lua's string capabilities actually find a sweet spot between "just concatenation" and the full complexity of regular expressions. String formatting capability is very strong, and accumulating strings through "buffers" or tables is simple and efficient.
String scanning is, in my opinion, one of the best parts of the design. It doesn't have "or" patterns but otherwise gives you a large fraction of what you get from regular expressions, including a very powerful and elegant "capture" function. For example, I can convert a string to hex by capturing every single character and applying a function to it:
s:gsub('.', function(c) return string.format("%02x", string.byte(c)) end)
Or I can escape non-alphanumeric, non-space characters into octal:
s:gsub('[^%w%s]', function(c) return string.format([[\%03o]], string.byte(c)) end)
Some of the features on display here:
The escape character for string scanning is %, which is different from the escape character for string quoting, which is \. This decision is brilliant and should win an award by itself :-)
There are multiple mechanisms for quoting literal strings, including [[...]] in which no characters have to be escaped. If you want to generate or match strings with backslashes in them (like LaTeX for example), this is a godsend.
If you want the full power of a context-free parser, you can always use LPEG, a library written by one of Lua's designers.
Performance is pretty important (especially startup time)
Lua consistently wins performance awards. Startup is lightning fast: the whole system (including compiler, library, garbage collector, and runtime system) fits in 150KB. To avoid pause times, Lua provides incremental garbage collection. See also SO question Why is Lua faster than other scripting languages?
You can make startup even faster by precompiling your scripts, but I've never found it necessary to do this—and because compiled code (as opposed to source code) is not portable, precompilation usually creates more headache than it solves.
Needs easily be compiled on multiple platforms
Lua compiles using pure ANSI C and does not even require POSIX. I have a version running on my PalmOS PDA.
Needs to be a language which will still be around in 5 years time.
Lua has been around since 1993. Moreover, the two members of the team who provide the most support are tenured professors at PUC-Rio. Lua is their livelihood. Finally, the whole system is only 17,000 lines of code. If Rio fell off the map tomorrow, anybody with a good undergraduate compiler course could pick the system up and maintain it. There would be plenty of volunteers.
I've looked a little at Python and Lua but don't really know enough about them
See SO question Which game scripting language is better to use: Lua or Python?.
People have been embedding tcl in larger projects for what seems like ages. It's been a while since I've had to use tcl for anything...
One of the things that sets tcl apart from other programming languages is that everything is a string.
And for your reference, here's the tcl documentation on string functions.
tcl might be easier to embed than perl, but I do have to agree #Matthew Scharley's reasoning. Also, tcl isn't exactly known for it's performance, but maybe that's changed in recent years.
Anyway, here is the tcl wiki link on embedding tcl in C applications, and a relevant quote from the page:
"How do I embed a Tcl interpreter in my existing C (or C++) application?" is a very frequently-asked question. It's straightforward, certainly far easier than doing the same with Perl or, in general, Python; moreover, this sort of "embeddability" was one of the original goals for Tcl, and many, many projects do it. There are no complete discussions of the topic available, but we can give an overview here. (RWT 14-Oct-2002)
Another alternative might be to go with Lua, as you mentioned, while extending it with another C string library of your choice (Google turns up The Better String Library, for instance).
Once you've compiled Lua into your application, you can "extend" C functions to Lua's interpreter. Or maybe the built-in string functions are adequate for you.
You certainly have a few options.
We looked at both Python and Lua for scripting for a .NET product. The goal was to provide some scripability for end users. The decision came down to Python because the powers-that-be preferred anything with Microsoft support to everything else. My choice was for Lua.
There's a good survey paper on the relative merits of the embedding APIs of various scripting languages:
H. Muhammad and R. Ierusalimschy. C APIs in extension
and extensible languages. Journal of Universal Computer
Science, 13(6):839–853, 2007.
Looking at combining both excellent string manipulation and an excellent embed API, I would suggest, in order:
Ruby: Excellent string support, including syntax support for regex. Well-designed embed API, very easy to use.
Lua: I'm not sure how its string support is, but its supposed to be a great language for embedding.
Python: Less easy to embed, slightly harder to use string features than Ruby. But it has Pyrex, so that might be an easier way to embed it.
PHP: Nasty API, nasty language. The embed SAPI is really a second-class citizen, but it does work. There are a lot of string manipulation functions. Still, I wouldn't recommend it.
Perl: Nasty to embed (so far as I've heard), string support could be better.
I can't comment about TCL, but I hear its designed for embedding.
Python is not heavyweight at all! It's quite simple to embed (here's the official guide, but you can find many tutorials as well), very powerful, great for string processing, and a pleasant and easy language to use overall. It has a huge user community and support base, which is a bonus.
Python has also been embedded into a large number of real-life applications. One cool example I can think of immediately is the Civilization IV game, most of which runs on Python scripts on top of a C++ API.
Some people may disagree but Sara Goleman has published a great book on extending and embedding PHP. Which is becoming one of the most widely used languages around... :)
PHP String support isn't as great as say Perl, but it's very usable.
Did I mention it's written in C?
</my2cents>
Perl. Its (original) reason for being is string manipulation.