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I am exposed to C because of embedded system programming, and I think it's one wonderful language in this field. However, why is it used to write compilers? If the reason why gcc is implemented in C/C++ is that there aren't many good languages at that time, there's no excuse for why clang is taking the same path (using C/C++).

Is it for performance reasons? Mostly interpreted languages are a bit slower compared with compiled languages, but I guess the difference is almost negligible in CoffeeScript (JavaScript), because of Node.js.

From the perspective of developers, I suppose it's much easier to write one compiler using high level languages. Unfortunately, most of compilers out there are written in C/C++. Is it just because of legacy code?

Response to comments:

  • Bootstrapping is just one way to illustrate that this language is powerful enough to write one compiler. It shouldn't the dominant reason why we choose the language to implement the compiler.

  • I agree with the guess given below, that "most compiler developers would answer because most of compiler related tools (bison, yacc) emit C code". However, neither GCC nor Clang use generated parser, they implemented one themselves. This front-end process is independent of targeting architecture, and should not be C/C++'s strength.

  • There's more or less consensus that performance is one key factor. Indeed, even for GCC and Clang, building a reasonable size of C project (Linux kernel) takes a lot of time. Is it because of the front-end or the back-end. I have to admit that I didn't have much experience on backe-end of compilers, as we finished the course on compiler with generated LLVM code.

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    C++ is a high level language if you want to use it as such. It's low level too if you need that. (And you'd have to back up that performance assertion for CoffeeScript (or anything else) in the context of compiler workloads to make it meaningful.) Commented Jun 20, 2013 at 14:37
  • JavaScript is "too high-level", so to say. How would you, for example, implement integers with different width (where most JavaScript implementations only have floating-point numbers, or integers with non-controllable size)? JavaScript's dynamism and dynamic object-oriented nature has some performance drawbacks as well. A hash table in which you can use integers and floating-point numbers and strings and functions as keys will still need a hash function even if compiled down to native code using JIT. Commented Jun 20, 2013 at 15:00
  • @H2CO3 Suppose Javascript is used to translate C code to machine code. Why would the translator have to worry about producing integers of different widths, when the translator doesn't even need to exist at runtime? I think Javascript would be a suitable programming language for a compiler. The presence of associative arrays makes it easy to produce a syntax parsing tree. Commented Jun 20, 2013 at 15:20
  • @undefinedbehaviour Perhaps you never wrote a string-handling function in C, but if you want to compare a char to an int, you need zero-extending. Similarly, if you declare an array of short or long long, you also do need to worry about width of integers. Commented Jun 20, 2013 at 15:25
  • Why I write compilers in C++ and not JS/Coffee: static-typing, multi-threading, automatic and deterministic resource management, performance, native data types (e.g. uint16_t, size_t), ....... Commented Oct 5, 2016 at 17:34

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I am exposed to C because of embedded system programming, and I think it's one wonderful language in this field.

Yes. It's better than Java.

However, why is it used to write compilers?

This question can't be answered without asking the developers. I suspect that the majority of them will tell you that common compiler-writing software (yacc, flex, bison, etc) produce C code.

If the reason for gcc is that there aren't many good languages, there's no excuse for clang.

GCC isn't a programming language, and neither is Clang. They're both implementations of the C programming language.

Is it for performance reasons?

Don't confuse implementation with specification. Speed is an attribute introduced by your compiler and your computer, not by the programming language. GCC happens to produce fairly efficient machine code, which might influence developers to use C as their primary programming language... but in ten years time, it could* be that node.js produces more efficient machine code than GCC. Don't forget, StackOverflow is forever.

* could, but most likely won't. See Ira Baxters comment below for more info.

Mostly interpreted languages are a bit slower compared with compiled languages, but I guess the difference is almost negligible in CoffeeScript (JavaScript), because of Node.js.

Similarly, interpretation or compilation isn't the choice of the language, but of the implementation of the language. For example, GCC and Clang choose to compile C to machine code. Ch and CINT are two interpreters that translate C code directly to behaviour, rather than machine code. Java was once predominantly translated using interpretation, too, but is now predominantly compiled into JVM bytecode. Javascript seems to be phasing towards predominant compilation, too. Who knows? Maybe you'll see compilers written predominantly in Javascript in ten years time...

From the perspective of developers, I suppose it's much easier to write one compiler using high level languages.

All of these programming languages are technically high level. They're mostly defined in terms of an abstract machine; They're certainly not low level.

Unfortunately, most of compilers out there are written in C/C++.

I don't consider it unfortunate that C++ is used to write software; It's not a bad programming language.

Is it just because of legacy code?

I suppose legacy code might influence the decision of a programmer. In the end though, as I said, you'd have to ask the developers. They might just decide to use C or C++ because C or C++ is their favourite programming language... Why do you speak English?

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"but in ten years time, it could be that node.js produces more efficient machine code than GCC". Yes, in the realm of possible but not in the realm of probable. To out-compile GCC, the research community will have to solve many hard problems for analyzing dynamic langauges, and those problems have resisted solutions for 30 years now, so it isn't like the answers are around the corner. If you want a high-performance compiler, you're more probable to get it if you build it in C++ than Java/Coffee/foobarScript.
Don't confuse implementation with specification. Speed is determined by the compiler not the language itself. However, mostly, we will just say one language is faster or slower that the other, even though we mean it's the executable generated by the compiler. I do believe that some low level languages are faster than high level languages because they let developers to write architecture specific code. Whether this is good or bad is another story.
@zerm That comment, though inspired by lack of sense of humour, is itself comedic gold. I wish I could upvote twice :D Do you like object resurrection? As I understand in Java an objects destructor is only ever invoked once, so doesn't that constitute a means for memory leaks?
Ohh and gotta love those insanely long identifiers! Mmm lotsa tongue twisters in Java!
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Compilers are very complex software in general. The front end part is pretty simple (parsing), but the backend part (scheduling, code generation, optimizations, register allocations) involve NP-complete problems (of course compilers try to approximate solutions to these problems). Thus, implementing in C would help compile times. C is also very good at bitwise operators and other low level stuff, which is useful for writing a compiler.

Note that not all compilers are written in C though. For example, Haskell GHC compiler is written in Haskell using bootstrapping technique.

Javascript is async, which doesn't suit compiler writing.

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I see many reasons:

  • There is no elegant way of handling bit-precise code in Javascript
  • You can't write binary files easily in Javascript, so the assembler part of the compiler would have to be in a more low-level language
  • Huge JS codebase are very heavy to load in memory (that's plain text, remember?)
  • Writing optimizing routines for compilers are heavily CPU-intensive, which is not yet very compatible with Javascript
  • You wouldn't be able to compile your compiler with it (bootstrap), because you need a Javascript interpreter behing your compiler. The bootstrap phase wouldn't be "pure":
    JS Compiler compiles NodeJS -> NodeJS runs your new Compiler -> new JS Compiler
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gcc is implemented primarily in C, but that is not true of all compilers, including some that are quite standard. It is a common pattern for a compiler to be implemented in the language that it compiles. ghc is written largely in Haskell. Recent versions of guile feature a compiler implemented mostly in Scheme.

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nope, coffeescript et al are still much slower than natively-compiled (and optimised) C code. Even if you take the subset of javscript that is able to be optimised (asm.js) its still twice as slow as native C.

What you hear about when people say node.js is just as fast as C code means that its just as fast as part of an overall system that does other things like read from disk, wait for data off the network, etc. In these systems the CPU is underused (especially with today's superfast CPUs) so the performance problem is not the raw processing capability of the language. Hence, a node.js server is exactly as fast as a C server if they're both stuck waiting for a network call to return data. The type of system written in node.js does a lot of waiting for network which is why people use node.js. The type of system written in C does not suit being written in node.js

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"Native C"? The semantic descriptions in this International Standard describe the behavior of an abstract machine in which issues of optimization are irrelevant.

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