Spock levels of fascinating from me. I want to learn how to compile a pdp11 emulator on my mac.
replies(4):
Works great on Apple Silicon
E.g. since the MAME project considers itself living documentation of arcade hardware, it would be more properly classified as a simulator. While the goal of most other video game emulators is just to play the games.
In practice the terms are often conflated.
definitely agree on simulator though!
Intepreter either writes it in bytecode and then executes the bytecode line by line ?
Atleast that is what I believe the difference is , care to elaborate , is there some hidden joke of compiler vs intepreter that I don't know about ?
It just feels that one is emulator if its philosophy is "it just works" and simulator if "well sit down kids I am going to give you proper documentation and how it was built back in my days"
but I wonder what that means for programs themselves...
I wonder if simulator==emulator is more truer than what javascript true conditions allow.
Calling the same thing a different name.
The goals merely overlap, which is obvious. Equally obviously, if two goals are similar, then the implimentations of some way to attain those goals may equally have some overlap, maybe even a lot of overlap. And yet the goals are different, and it is useful to have words that express aspects of things that aren't apparent from merely the final object.
A decorative brick and a structural brick may both be the same physical brick, yet if the goals are different then any similarity in the implimentation is just a coincidense. It would not be true to say that the definition of a decorative brick includes the materials and manufacturing steps and final physical properties of a structural brick. The definition of a decorative brick is to create a certain appearance, by any means you want, and it just so happens that maybe the simplest way to make a wall that looks like a brick wall, is to build an actual brick wall.
If only they had tried to make it clear that there is overlap and the definitions are grey and fuzzy and open to personal philosophic interpretation and the one thing can often look and smell and taste almost the same as the other thing, if only they had said anything at all about that, it might have headed off such a pointless confusion...
For compilers, constant folding is a pretty obvious optimization. Instead of compiling constant expressions, like 1+2, to code that evaluates those expressions, the compiler can already evaluate it itself and just produce the final result, in this case 3.
Then, some language features require compilers to perform some interpretation, either explicitly like C++'s constexpr, or implicitly, like type checking.
Likewise, interpreters can do some compilation. You already mentioned bytecode. Producing the bytecode is a form of compilation. Incidentally, you can skip the bytecode and interpret a program by, for example, walking its abstract syntax tree.
Also, compilers don't necessarily create binaries that are immediately runnable. Java's compiler, for example, produces JVM bytecode, which requires a JVM to be run. And TypeScript's compiler outputs JavaScript.
I don't know what the difference is , I know there can be intepreters of compilers but generally speaking it's hard to find compilers of intepreters
Eg C++ has compilers , intepreters both (cpi) , gcc
Js doesn't have compilers IIRC , it can have transpilers Js2c is good one but i am not sure if they are failsafe (70% ready) ,
I also have to thank you , this is a great comment
A compiler processes the code and provides an intermediate result which is then "interpreted" by the machine.
So to take the "writes it in byte code" -- that is a compiler. "executes the byte code" -- is the interpreter.
If byte code is "machine code" or not, is really secondary.
The same tool can often be used to do both. trival example: a web browser. save your web page as a pdf? compiler. otherwise interpreter. but what if the code it is executing is not artisanal handcrafted js but the result of a typescript compiler?
As for the comparison with the JVM .. compare to a compiler that produces x86 code, it cannot be run without an x86 machine. You need a machine to run something, be it virtual or not.
A compiler takes the same thing, but produces an intermediate form (byte code, machine code, another languages sometimes called "transpilar"). That you can then pass through an interpreter of sorts.
There is no difference between Java and JVM, and Python and the Python Virtual Machine, or even a C compiler targeting x86 and a x86 CPU. One might call some byte code, and the other machine code .. they do the same thing.
* The first axis is static vs dynamic types. Java is mostly statically-typed (though casting remains common and generics have some awkward spots); Python is entirely dynamically-typed at runtime (external static type-checkers do not affect this).
* The second axis is AOT vs JIT. Java has two phases - a trivial AOT bytecode compilation, then an incredibly advanced non-cached runtime native JIT (as opposed to the shitty tracing JIT that dynamically-typed languages have to settle for); Python traditionally has an automatically-cached barely-AOT bytecode compiler but nothing else (it has been making steps toward runtime JIT stuff, but poor decisions elsewhere limit the effectiveness).
* The third axis is indirect vs inlined objects. Java and Python both force all objects to be indirect, though they differ in terms of primitives. Java has been trying to add support for value types for decades, but the implementation is badly designed; this is one place where C# is a clear winner. Java can sometimes inline stack-local objects though.
* The fourth axis is deterministic memory management vs garbage collection. Java and Python both have GC, though in practice Python is semi-deterministic, and the language has a somewhat easier way to make it more deterministic (`with`, though it is subject to unfixable race conditions)
I have collected a bunch more information about language implementation theory: https://gist.github.com/o11c/6b08643335388bbab0228db763f9921...
It is a tiny distinction, but generally I'd say that a simulator tries to accurately replicate what happens on an electrical level as good one can do.
While an emulator just does things as a black box ... input produces the expected output using whatever.
You could compare it to that an accurate simulator of a 74181 tries to do it by using AND/OR/NOT/... logic, but an emulator does it using "normal code".
In HDL you have a similar situation between structural, behavioral design ... structural is generally based on much more lower level logic (eg., AND/NOR/.. gates ...), and behavioral on higher logic (addition, subtraction ...).
"100%" accuracy can be achieved with both methods.