Comment by sieve
2 days ago
> If all you do is construct an AST and interpret it it's not really a compiler is it.
What if I dumped the AST to disk, called it "bytecode" and updated the "interpreter" to run this "bytecode"? Would you consider that to be a compiler? :-)
> where X includes
I don't consider any of these things to be essential. There are entire languages out there which run on interpreters of some kind. There are others which compile down to C/JS. Many compilers use LLVM as their backend. By your definition, none of them use (or are) compilers.
> Would you consider that to be a compiler? :-)
:) No. Under my definition there needs to be some non-trivial transformation into or out of an intermediate and/or target representation (either syntax-directed directly out of the parser, or from a materialized AST). Personally I would argue that even if you trivially "compiled" to sequential bytecode, if the bytecode is then interpreted it is hard to argue that you have created a compiler (the pre-JIT cpython interpreter is still an interpreter, even though it includes a bytecode representation). But I can see that this point can be argued, and historically a school exercise of writing a Pascal-to-pcode converter would be called a compiler, so sure, you can take that perspective if you like. Just don't get confused about whether you are learning to build a compiler (definition 1) or a compiler (definition 2).
I have written all kinds of compilers, interpreters and vms over the last 15 years. A couple of them for work. The rest for fun. Some vms used RC, others did mark-and-sweep GC. Some vms even did JIT. A lot of them were simple treewalk interpreters because the point was to play with the syntax of the language.
Based on that experience, I would say your definition is more academic than realworldly as javac (or any compiler targeting the JVM) is not a real compiler according to it.
> javac (or any compiler targeting the JVM) is not a real compiler according to it
I think it depends on how you interpret my "non-trivial transformation into or out of an intermediate and/or target representation". For example if javac involves IR, SSA based analysis and transformation (which I assume it does) then that would be a non-trivial transformation and I'd call it a compiler. If on the other hand it was a direct syntax-directed transformation to java byte code then I'd call it a translator not a compiler. But I'm not claiming any authority over definitions here. Words aren't my strong suit.
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