Chez is not JITted. Chez compiles to native binaries that run win the chez runtime (so not stand-alone).
> Whether compiling on the fly or precompiling, the compiler produces optimized machine code, with some optimization across separately compiled library boundaries. [0]
> Chez Scheme compiles source forms as it sees them to machine code before evaluating them, i.e., "just in time." [1]
Chez can both JIT and pre-compile. But it absolutely has a JIT, and has had as far back as I could trace.
Take a hypothetical example: (for ([i (in-range a b c)]) (display i)). At compile time, chez has no way to know whether c is positive or negative (if it is set at runtime), thus making each iteration check whether c is positive or negative. In racket such code has negligible performance impact because the runtime will generate native code "just in time" with optimizations deduced from run-time information.
The JIT of chez is just a side effect of the AOT being fast enough to run on the fly. SBCL does the same.
Huh? Then what do you consider a JIT?
> In computing, just-in-time (JIT) compilation, also known as dynamic translation, is a way of executing computer code that involves compilation during execution of a program – at run time – rather than prior to execution. Most often, this consists of source code or more commonly bytecode translation to machine code, which is then executed directly. [0]
It is just fast enough that AOT compilation isn't a noticeable delay even at the repl.
Cisco says Chez compiles code just before it uses it, at runtime:
> Chez Scheme compiles source forms as it sees them to machine code before evaluating them, i.e., "just in time."
They refer to it as a "incremental native compiler". Incremental compilation happens at runtime. An incremental compiler that runs at runtime is a form of JIT compiler.
> JIT compilation is a combination of the two traditional approaches to translation to machine code – ahead-of-time compilation (AOT), and interpretation – and combines some advantages and drawbacks of both
Everything I know and Wiki says that is a JIT.
Are you saying it isn't a JIT because it isn't a tracing JIT? Bearing in mind tracing JITs came about in the 70s, but JITs themselves are about a decade older.
Do we at least agree that Chez does not generate code at runtime? Because I am very certain it does not (I have spent a lot of time with the chez codebase)
If you still want to call it a JIT then every language that compiles code to an intermediate representation and then executes it is a JIT language,which means just about every friggin language.
I have also ported a non-trivial amount of code making use of rackets JIT optimizations (based on hot paths) to Chez and have spent a lot of time compensating for the lack of the same optimizations in Chez.
SBCL compiles code fast enough to not have a distinct compilation step for most software in a way similar to chez and no one would consider it a JIT.
Edit:
Let me quote Andy Keep (akeep on github. One of chez schemes developers):
Chez Scheme does compile at the REPL, but in general I would not call it a JIT compiler. It just compiles everything the same way regardless of if you are compiling it ahead of time or while you are running in an interactive session.
https://groups.google.com/forum/m/?utm_source=digest&utm_med...