Polyglot.jl: transparent remote/recursive evaluation between languages

The Julia module Polyglot.jl supports transparent remote/recursive evaluation between Julia and another interpreter through automatic call serialization.

In poorer words, Polyglot.jl lets you call functions in other languages as they were regular Julia functions. It also allows other languages to call Julia functions as if they were native.

Remote output is also transparently redirected locally, and since the evaluation is performed through a persistent co-process, you can actually spawn interpreters on different hosts through “ssh” efficiently.

Polyglot.jl currently supports PHP, Perl, JavaScript (Node.js) and Python.

Polyglot.jl is currently a work-in-progress. Suggestions about API design are highly appreciated: we’re looking for a consistent calling interface between regular Julia’s multiprocessing and other external language bridges.

As an additional note, while Polyglot.jl can be used with Python, it’s definitely not as sophisticated or as efficient as PyCall. If you don’t need to run multiple/remote/mixed Python instances (for example, to mix major Python versions or to use PyPy), using PyCall is advisable.

Releases

This module is registered in the main Julia Package Repository. See Julia’s Pkg module for installation instructions.

Releases are ephemeral at the time of writing. Julia 0.3 is supported, but all development is performed with Julia 0.4.

All the relevant source/developer information can be found on Github:

https://github.com/wavexx/Polyglot.jl

Overview

Polyglot.jl can communicate with another interpreter by “bonding” with it:

julia> # Let's bond with a PHP interpreter
julia> using Polyglot;
julia> php = bond!("PHP");
julia> reval(php, "echo \"Hello world!\\n\""; block=true);
Hello world!

julia> # Make an expensive split function using PHP's explode
julia> explode = importfn(php, "explode");
julia> explode(" ", "Hello world splitted by PHP!")
5-element Array{Any,1}:
 "Hello"
 "world"
 "splitted"
 "by"
 "PHP!"

julia> # Call Julia from PHP
julia> call_me() = println("Hi, this is Julia talking!");
julia> exportfn(php, call_me);
julia> reval(php, "call_me()");
Hi, this is Julia talking!

julia> # Bridge two worlds!
julia> perl = bond!("Perl");
julia> proxyfn(php, "explode", perl);
julia> # note: explode is now available to Perl, but still executes in PHP
julia> reval(perl, "explode(\"=\", \"Mind=blown!\")")
2-element Array{Any,1}:
 "Mind"
 "blown!"

API

Initialization

Bonds can be constructed by using the bond!() function:

using Polyglot
interpreter = bond!("language")

The first argument should be the desired language name (“JavaScript”, “PHP”, “Perl”, “Python”). The list of supported languages can be fetched dynamically using Polyglot.list_drivers().

You can override the default interpreter command using the second argument, which allows to specify any regular command to be executed:

using Polyglot
py = bond!("Python", `ssh remote python3`)

An additional list of arguments to the interpreter can be provided using the third argument, args:

using Polyglot
py = bond!("Python", `ssh remote python3`, String["-E"; "-OO"])

The optional arguments are just strings. They are quoted and appended to the main command after default arguments.

Default arguments may be supplied automatically by the driver to force an interactive shell; for example “-i” is supplied if Python is requested. You can disable default arguments by using def_args=False.

The following keyword arguments are supported:

cwd:

Working directory for the interpreter (defaults to current working directory).

env:

Environment for the interpreter (defaults to ENV).

def_args:

Enable (default) or suppress default, extra command-line arguments to the interpreter.

timeout:

Defines the timeout for the underlying communication protocol. Note that bond!() cannot distinguish between a slow call or noise generated while the interpreter is set up. Defaults to 60 seconds.

trans_except:

Warning

Unimplemented

Enables/disables “transparent exceptions”. Exceptions are always first class, but when trans_except is enabled, the exception objects themselves will be forwarded across the bond. If trans_except is disabled (the default for all languages except Julia), then local exceptions will always contain a string representation of the remote exception instead, which avoids serialization errors.

Exported functions

reval(bond, code; block=false)

With block=false (the default), evaluate and return the value of a single statement of code in the top-level of the interpreter.

With block=true instead, evaluate a code block in the top-level of the interpreter. Any construct which is legal by the current interpreter is allowed. Nothing is returned.

rref(bond, code):

Return a reference to an single, unevaluated statement of code, which can be later used in reval() or as an immediate argument to rcall(). See Quoted expressions.

close(bond):

Terminate the communication with the interpreter.

rcall(bond, name, args...):

Call a function “name” in the interpreter using the supplied list of arguments *args (apply *args to a callable statement defined by “name”). The arguments are automatically converted to their other language’s counterpart. The return value is captured and converted back to Julia as well.

importfn(bond, name):

Return a function that calls “name”:

explode = importfn(bond, "explode")
# Now you can call explode as a normal, local function
explode(" ", "Hello world")

exportfn(bond, func, name):

Export a local function “func” so that can be called on the remote language as “name”. If “name” is not specified, use the local function name directly. Note that “func” must be a local function, not a function name.

proxyfn(bond, name, other_bond, other_name):

Export a remote function “name” from “bond” to “other_bond”, named as “other_name”. If “other_name” is not provided, the same value as “name” is used:

php = bond!("PHP")
py = bond!("Python")
proxyfn(php, "explode", py)

interact():

Warning

Unimplemented

Start an interactive session with the underlying interpreter.

Exceptions

BondException:
Thrown during bond!() initialization or unrecoverable errors.
BondTerminatedException:
Thrown when the bond exits unexpectedly.
BondSerializationException:
Thrown when an object/exception which is sent or received cannot be serialized by the current protocol. The remote record can be either false (when attempting to send) or true (when receiving). A BondSerializationException is not fatal.
BondRemoteException:
Thrown for uncaught remote exceptions. The “data” record contains either the error message (with trans_except=False) or the remote exception itself (trans_except=True).

Beware that both BondSerializationException (with remote==true) and BondRemoteException may actually be originating from uncaught local exceptions when an exported function is called. Pay attention to the error text/data in these cases, as it will contain several nested exceptions.

Quoted expressions

Polyglot.jl has minimal support for working with quoted expressions, through the use of rref(). rref() returns a reference to a unevaluated statement that can be fed back to reval() or as an immediate (i.e.: not nested) argument to rcall(). References are bound to the interpreter that created them.

rref() allows to “call” methods that take remote un-serializable arguments, such as file descriptors, without the use of a support function and/or eval:

pl = bond!("Perl")
reval(pl, "open(\$fd, \">file.txt\");"; block=true)
fd = rref(pl, "\$fd")
rcall(pl, "syswrite", fd, "Hello world!")
rcall(pl, "close", fd)

Since references cannot be nested, there are still cases where it might be necessary to use a support function. To demonstrate, we rewrite the above example without quoted expressions, while still allowing an argument (“Hello world!”) to be local:

pl = bond!("Perl")
reval(pl, "open(\$fd, \">file.txt\");"; block=true)
reval(pl, "sub syswrite_fd { syswrite(\$fd, shift()); };", block=true)
rcall("syswrite_fd", "Hello world!")
reval("close(\$fd)")

Or more succinctly:

rcall(pl, "sub { syswrite(\$fd, shift()); }", "Hello world!")

General/support mailing list

If you are interested in announcements and development discussions about Polyglot.jl, you can subscribe to the bond-devel mailing list by sending an empty email to <bond-devel+subscribe@thregr.org>.

You can contact the main author directly at <wavexx@thregr.org>, though using the general list is encouraged.