Extension Points, or how OCaml is becoming more like Lisp

https://blogs.janestreet.com/extension-points-or-how-ocaml-is-becoming-more-like-lisp/?utm_source=rss&utm_medium=rss&utm_campaign=extension-points-or-how-ocaml-is-becoming-more-like-lisp

by edwintorok • 12 years ago

104 29 12 years ago

blogs.janestreet.com

edwintorok• 12 years ago

It would be interesting to see how the speed of -ppx extensions compares to camlp4. If camlp4 is run in bytecode mode it can be quite slow, I looked at 'top' while running 'opam install core' at some point, and most of the time was taken by camlp4. Since -ppx extensions are supposed to run natively (without requiring natdynlink support even) I would expect them to be faster.

Has anyone done any comparisons?

avsm2• 12 years ago

There are pros and cons to not using dynlink, since it requires another fork (although this can be avoided using a custom compiler driver).

Avoiding bytecode in the compilation toolchain is really the main benefit though. This was originally due to the fact that only the bytecode backend supported dynamic loading (which is used by camlp4 to load the syntax extension modules). When native dynamic code loading was added to OCaml circa 2009 or so, the build systems around camlp4 never really took up the change to switch to the much faster native code version. All the ppx extensions emerging now are at least guaranteed to have a native code version on all the major supported architectures (x86, ARM, Sparc, PPC)

obamacaress• 12 years ago

been writing OCaml since years. Def good news

pjmlp• 12 years ago

Interesting, seem similar to annotations/attributes. Also some similarity with AST handling in other languages.

Now I have something to play with on the upcoming weekend. :)

p4bl0• 12 years ago

I'm not convinced by the example given at the end of the article. For this precise very simple use case it might be ok, but what about more complicated syntax extensions?

avsm2• 12 years ago

Camlp4 is still very much around and maintained out of tree, and will work in the next release of OCaml (https://github.com/ocaml/camlp4). Extension points are intended to be simpler and more easily integrated into editors for the common case, but you can still use camlp4 for extensions that genuinely extend the OCaml grammar.

wes-exp3• 12 years ago

As languages improve, they keep moving towards Lisp — a story that has been playing out for decades. There is a reason Lisp is called "the final language".

yminsky• 12 years ago

I think Lisp and Scheme have excellent macro systems, which are eminently worth stealing. I don't think OCaml will evolve into them on the type-system level though...

hajile2• 12 years ago

Shen lisp has the world's only turing complete type system (making it even more advanced than Haskell's system).

emiljbs2• 12 years ago

The thing about the OP is that Lisp isn't well defined. The only constant is that what Lisp is changes, so it's really not that useful to talk about Lisp as "the final language" because there will always be new Lisps. The only common thing between the Lisps seems to be the s-expressions and metaprogramming.

lmm3• 12 years ago

Only if you're looking from a particular angle. Given the growth of more and more powerful type systems I'd say there's an important sense in which, as languages improve, they keep moving away from Lisp.

This story isn't really OCaml becoming more like Lisp; rather, it's OCaml finding a way to implement Lisp's best feature without the downsides of being Lisp.

wes-exp3• 12 years ago

Only if you're looking from a particular angle

I'd say most angles except the type system as you point out, or am I missing something?

lispm2• 12 years ago

One thing that's not nice in typical Lisp macros: for really complex transformations one needs a code walker. Unfortunately that part has a few problems: no standard code walker, complex api, different ways to access crucial information about the code in various implementations, ...

rwmj• 12 years ago

OCaml has a type-safe AST walker (two actually - one is part of camlp4 and the other called ocaml-ast-analyze).

a-nikolaev• 12 years ago

Cool. Language extensions are easier to write. Honestly, never had the guts to really learn camlp4 beyond an introductory tutorial, so I am happy to hear that this new approach is easier and also more practical.

There is a link from the article with a more complete example of how the extension points really work: http://whitequark.org/blog/2014/04/16/a-guide-to-extension-p...

OCaml is great because it is doing a lot of things right. Hope, this new feature will become more widely used than camlp4, and become a stable feature of the language.

Extension Points, or how OCaml is becoming more like Lisp

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