4 ms·

Caramel: An OCaml to Erlang Compiler

151 points by signa11 6y ago

brightball 6y ago
Can this work? People have been scrambling for static typing on the BEAM for a while. Is this the one?
- filmor 6y ago
  As far as I'm aware there are a few major problems with static typing in Erlang that can't be solved so far and are not solved here either: 1. If you have a function that calls into other modules like `other_module:some_func(X)`, then the typing of this call can change at runtime. You could first have some_func(N) when is_number(N) -> N + 1. and later load a new version with some_func(N) when is_integer(N) -> N + 1. The older version accepts all numbers, i.e. floats and integers, while the second only accept integers. 2. Erlang message passing can not be typed statically in a meaningful (i.e. non-trivial) way, as the typing may be state-dependent: Pid = spawn_link(fun () -> receive first -> ok; _ -> error(bad_message) end, receive second -> ok; _ -> error(bad_message) end end) Now, the static typing of sending to `Pid` depends on what you've sent before. This could maybe be handled by "enumerating" the receives, but I think that invites the halting problem into your type system.
  - mikhailfranco 6y ago
    The stateful receive (2) just means that an Erlang process should be modelled as a state machine with some variety of automaton. Each receive blocks on a finite ordered sequence of (possibly overlapping) pattern-matching expressions. The priority sequence means it behaves more like a PEG than an NDA or DFA. Writing down the PEG message grammar for the process becomes quite easy. Pattern matching is well-defined. The number of states may be large, but can often be factored nicely by data types and ranges (e.g. tagged tuples). However, PEG semantics make it difficult to analyze composition of receive statements in the general case. It's easy to solve the Halting Problem in Erlang - just add a timeout to your receive and accept some false positives :)
    - filmor 6y ago
      This is about static typing. I expect my static typing to terminate. Getting typing to work with a "screw this" fallback is already possible.
      - mikhailfranco 6y ago
        Have a look at Erlang's success typing https://it.uu.se/research/group/hipe/papers/succ_types.pdf https://it.uu.se/research/group/hipe/papers/succ_types.pdf
        filmor 6y ago
        Yes, that is the "screw-this-fallback" typing I was referring to... If it fails to prove a type for a value, it falls back to "this could be any type" which brings this part of the code back to pure dynamic typing.
macintux 6y ago
Obligatory link to my list of alternative BEAM languages. https://gist.github.com/macintux/6349828#alternative-languages-targeting-the-erlang-vm https://gist.github.com/macintux/6349828#alternative-languag...
- lactobacillis 6y ago
  Does Swish (https://github.com/becls/swish https://github.com/becls/swish) fit anywhere in your list?
  - macintux 6y ago
    Thanks, I added it to the list of other actor implementations.
- scns 6y ago
  There is https://nact.io/ https://nact.io/ for JS/ReasonML. For Rust there is: https://bastion.rs/ https://bastion.rs/ https://docs.rs/actix/0.10.0/actix/ https://docs.rs/actix/0.10.0/actix/ and Lunatic (which compiles to WebAssembly): https://news.ycombinator.com/item?id=25160474 https://news.ycombinator.com/item?id=25160474 (edit: added Actix and Lunatic, formatting)
  - macintux 6y ago
    Thank you very much, I've added all of those.
mcintyre1994 6y ago
If this works well, and can eventually interface nicely with Elixir libraries like Phoenix, I think it’ll be really exciting. Definitely going to keep an eye on this :)
natchy 6y ago
So does this mean you are effectively writing OCaml-looking erlang? meaning, you are using Erlang libraries (not OCaml libs) to perform any IO or iterate over a list? Where does OCaml end and Erlang begin?
- yawaramin 6y ago
  OCaml ends at compile time, Erlang begins at runtime.
  - natchy 6y ago
    yeah but WHAT is it compiling is my question. Does it compile OCaml dependencies or am I using Erlang deps?
    - yawaramin 6y ago
      It compiles a large subset of OCaml into (more or less) idiomatic Erlang. So technically it can compile a subset of OCaml dependencies, but I don't think it's integrated with the opam/dune package/build systems. It's still early days.
rubyn00bie 6y ago
So... does this work with distributed Erlang or hot code reloading? Because those are the reasons[1], to my knowledge, that statically typed language won't fly. Really stoked to give this a whirl! [1] I know, and in-case others don't, almost no one (literally) uses hot-code reloading. Still... Instead of killing it, as in the case of Lumen (I think), I'd like to see it become easier/better...
- filmor 6y ago
  Where do you derive this "almost no one" from? I use it all the time in production, and I guess quite a few other users use it to fulfill their very high uptime requirements.
  - macintux 6y ago
    I suspect there may be two different features (or degrees of features) here. Hot code reloading is indeed frequently used, but the corresponding ability to upgrade the entire application live (“hot swap”) is less so.
    - rkangel 6y ago
      I don't think so. Hot code reloading is hot code reloading. The parent to your comment is talking about in production so it's the 'real thing'.
      - macintux 6y ago
        I’m not sure what exactly you’re disputing. I would wager that nearly everyone who has run Erlang code in production has upgraded code (edit for precision: a module) live. To engineer the entire application to support an upgrade, and to do all the testing required to make sure it will work correctly, is very resource-intensive, and (lacking real numbers, just from observing the industry working for Basho) I’d wager very few people do so.
- rkangel 6y ago
  Users of hot code reloading are probably on the minority but there are definitely more than 'almost no-one'. There is a common misconception that 'no one on HN does something' means that 'no one does something'. HN is heavily biased towards startups and Web companies and large segments of the industry are very underrepresented. Pretty sure telecoms is one.
ErlangSolutions 6y ago
We will be running a webinar on Caramel on December 9th for those wanting to explore or ask the creator any questions :) Register at https://www2.erlang-solutions.com/webinar-registration-2 https://www2.erlang-solutions.com/webinar-registration-2

151 points by signa11 6y ago

brightball 6y ago

Can this work? People have been scrambling for static typing on the BEAM for a while. Is this the one?

filmor 6y ago
As far as I'm aware there are a few major problems with static typing in Erlang that can't be solved so far and are not solved here either: 1. If you have a function that calls into other modules like `other_module:some_func(X)`, then the typing of this call can change at runtime. You could first have some_func(N) when is_number(N) -> N + 1. and later load a new version with some_func(N) when is_integer(N) -> N + 1. The older version accepts all numbers, i.e. floats and integers, while the second only accept integers. 2. Erlang message passing can not be typed statically in a meaningful (i.e. non-trivial) way, as the typing may be state-dependent: Pid = spawn_link(fun () -> receive first -> ok; _ -> error(bad_message) end, receive second -> ok; _ -> error(bad_message) end end) Now, the static typing of sending to `Pid` depends on what you've sent before. This could maybe be handled by "enumerating" the receives, but I think that invites the halting problem into your type system.
- mikhailfranco 6y ago
  The stateful receive (2) just means that an Erlang process should be modelled as a state machine with some variety of automaton. Each receive blocks on a finite ordered sequence of (possibly overlapping) pattern-matching expressions. The priority sequence means it behaves more like a PEG than an NDA or DFA. Writing down the PEG message grammar for the process becomes quite easy. Pattern matching is well-defined. The number of states may be large, but can often be factored nicely by data types and ranges (e.g. tagged tuples). However, PEG semantics make it difficult to analyze composition of receive statements in the general case. It's easy to solve the Halting Problem in Erlang - just add a timeout to your receive and accept some false positives :)
  - filmor 6y ago
    This is about static typing. I expect my static typing to terminate. Getting typing to work with a "screw this" fallback is already possible.
    - mikhailfranco 6y ago
      Have a look at Erlang's success typing https://it.uu.se/research/group/hipe/papers/succ_types.pdf https://it.uu.se/research/group/hipe/papers/succ_types.pdf
      - filmor 6y ago
        Yes, that is the "screw-this-fallback" typing I was referring to... If it fails to prove a type for a value, it falls back to "this could be any type" which brings this part of the code back to pure dynamic typing.

macintux 6y ago

Obligatory link to my list of alternative BEAM languages. https://gist.github.com/macintux/6349828#alternative-languages-targeting-the-erlang-vm https://gist.github.com/macintux/6349828#alternative-languag...

lactobacillis 6y ago
Does Swish (https://github.com/becls/swish https://github.com/becls/swish) fit anywhere in your list?
- macintux 6y ago
  Thanks, I added it to the list of other actor implementations.
scns 6y ago
There is https://nact.io/ https://nact.io/ for JS/ReasonML. For Rust there is: https://bastion.rs/ https://bastion.rs/ https://docs.rs/actix/0.10.0/actix/ https://docs.rs/actix/0.10.0/actix/ and Lunatic (which compiles to WebAssembly): https://news.ycombinator.com/item?id=25160474 https://news.ycombinator.com/item?id=25160474 (edit: added Actix and Lunatic, formatting)
- macintux 6y ago
  Thank you very much, I've added all of those.

mcintyre1994 6y ago

If this works well, and can eventually interface nicely with Elixir libraries like Phoenix, I think it’ll be really exciting. Definitely going to keep an eye on this :)

natchy 6y ago

So does this mean you are effectively writing OCaml-looking erlang? meaning, you are using Erlang libraries (not OCaml libs) to perform any IO or iterate over a list? Where does OCaml end and Erlang begin?

yawaramin 6y ago
OCaml ends at compile time, Erlang begins at runtime.
- natchy 6y ago
  yeah but WHAT is it compiling is my question. Does it compile OCaml dependencies or am I using Erlang deps?
  - yawaramin 6y ago
    It compiles a large subset of OCaml into (more or less) idiomatic Erlang. So technically it can compile a subset of OCaml dependencies, but I don't think it's integrated with the opam/dune package/build systems. It's still early days.

rubyn00bie 6y ago

So... does this work with distributed Erlang or hot code reloading? Because those are the reasons[1], to my knowledge, that statically typed language won't fly. Really stoked to give this a whirl! [1] I know, and in-case others don't, almost no one (literally) uses hot-code reloading. Still... Instead of killing it, as in the case of Lumen (I think), I'd like to see it become easier/better...

filmor 6y ago
Where do you derive this "almost no one" from? I use it all the time in production, and I guess quite a few other users use it to fulfill their very high uptime requirements.
- macintux 6y ago
  I suspect there may be two different features (or degrees of features) here. Hot code reloading is indeed frequently used, but the corresponding ability to upgrade the entire application live (“hot swap”) is less so.
  - rkangel 6y ago
    I don't think so. Hot code reloading is hot code reloading. The parent to your comment is talking about in production so it's the 'real thing'.
    - macintux 6y ago
      I’m not sure what exactly you’re disputing. I would wager that nearly everyone who has run Erlang code in production has upgraded code (edit for precision: a module) live. To engineer the entire application to support an upgrade, and to do all the testing required to make sure it will work correctly, is very resource-intensive, and (lacking real numbers, just from observing the industry working for Basho) I’d wager very few people do so.
rkangel 6y ago
Users of hot code reloading are probably on the minority but there are definitely more than 'almost no-one'. There is a common misconception that 'no one on HN does something' means that 'no one does something'. HN is heavily biased towards startups and Web companies and large segments of the industry are very underrepresented. Pretty sure telecoms is one.

ErlangSolutions 6y ago

We will be running a webinar on Caramel on December 9th for those wanting to explore or ask the creator any questions :) Register at https://www2.erlang-solutions.com/webinar-registration-2 https://www2.erlang-solutions.com/webinar-registration-2