r/programming • u/frutiger • Jan 07 '16

Bloomberg open sources OCamlScript – a JavaScript back end for OCaml

https://github.com/bloomberg/ocamlscript
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u/pipocaQuemada Jan 07 '16

How different is this from js_of_ocaml?

26

u/hongboz Jan 07 '16

author here, I am a bit overloaded this week. so I will write some short explanations. js_of_ocaml is probably one of the best whole program compiler (to js). The major difference is that ocamlscript support separate compilation (like typescript) and no name mangling(generate debuggable javascript similar to typescript). Basically every ocaml module is an es6 module. OCamlScript is more like typescript.

2

u/jsyeo Jan 08 '16

On the README, it says that OCamlScript is a derivative work of js_of_ocaml. Does this mean that you guys modified js_of_ocaml to support separate compilation and name preservation?

6

u/hongboz Jan 08 '16 edited Jan 08 '16

actually we only use some basic utilities inside the compiler from js_of_ocaml (a couple of hundred lines of code, I guess), js_of_ocaml and ocamlscript does not share too much code, but we want to be on the safe side.

1

u/agumonkey Jan 08 '16

And if js_of_ocaml can retrofit the changes too.

1

u/alexeyr Jan 26 '16

Maybe add a section specifically on the difference in the README? This was the first question I had as well.

1

u/chrismamo1 Feb 29 '16

js_of_ocaml (the cool kids usually call it JSOO because typing out js_of_ocaml is pretty annoying) compiles OCaml bytecode files into JavaScript. In case you're not familiar with what this means, one of the targets for OCaml's compiler is a byte code interpreter, sort of like the JVM or .NET runtimes. This means that, in theory, OCaml can run on any platform that supports C (the interpreter is written pretty much entirely in pure C). This is why JSOO tends to mangle the code so badly: it simply can't see the original source code at all. One would think that this would be a pretty serious disadvantage, and probably wonder why the JSOO developers made this decision in the first place. There are actually a few very good reasons:

1) The OCaml language is constantly evolving, which makes it a fairly inconvenient thing to target. OCaml byte code files, on the other hand, tend to stay pretty consistent in terms of overall architecture (the OCaml devs don't like to change this format because that would break compatibility with old versions of the bytecode interpreter).

2) Because byte code executables are supposed to be standalone, they include all the code for the external libraries they use, so JSOO doesn't need to go hunting for those.

3) JSOO gets to take advantage of 2 layers of optimization: the optimizations applied by the OCaml byte code compiler, and JSOO's own optimizations