Erlang and Python

Following the suggestion that I try TwOtp, I've tried the "kicking the tyres" with that library.

Adapting the sample code to work against my own local node seemed easy enough:

from twisted.internet import reactor
from erlang import OneShotPortMapperFactory, buildNodeName

def gotConnection(inst):
    return inst.factory.callRemote(inst, "file", "get_cwd"
        ).addCallback(gotResult)

def gotResult(resp):
    print "Got response", resp
    reactor.stop()

def eb(error):
    print "Got error", error
    reactor.stop()

epmd = OneShotPortMapperFactory('client@chloe.ravnaandtines.com', "cookie")
epmd.connectToNode("servernode@chloe.ravnaandtines.com").addCallback(gotConnection).addErrback(eb)
reactor.run()

which involves rather more baggage than using IronPython against my tidying of the C# port of jinterface, for just a "hello world!", given that the jinterface-derived "hello world!" actually does more work (passing arguments, testing results):

import clr
clr.AddReference("OtpErlang.dll")
from System import Array

from Tinesware.Otp import *
import Tinesware.Otp.Erlang as Erlang

cNode = Self("clientnode@chloe.ravnaandtines.com", "cookie")
sNode = Peer("servernode@chloe.ravnaandtines.com")
connection = cNode.Connect(sNode)

args = Array[Erlang.IObject]([Erlang.Integer(1), Erlang.Integer(2)])

connection.SendRpc("mathserver", "add", args)
sum = connection.ReceiveRpc()

if  sum.Value.ToInt32() != 3:
  print "Assertion failed, returned = " + sum.Value
else:
  print "OK!"

And, like py_interface, I find that this doesn't "just work" either:

C:\Documents and Settings\Steve\My Documents\code\babel\erlang>python twotphw.py

Got error [Failure instance: Traceback (failure with no frames): <class 'erlang.epmd.NodeNotFound'>: 1]

which will require a similar amount of rolling sleeves up and getting hands dirty to resolve.

Erlang with Python and Ruby

Having played a bit with Erlang for real, in the sense of something non-trivial, even if not a complete product, I find I'm in the mood for more. But while it comes with some UI widgets, it's something more for headless use, and some client(s) in other languages doing the display.

To date, I can easily do Swing or WinForms as the UI toolkit -- but what about wxPython or FXRuby?

There are a number of bridges that I've found, but the closest to jinterface seem to be:

• py_interface for Python (about 2 years old)
• Un-named code drop on Google for Ruby (about 1 year old)

Neither of them have "just worked" for me in the way that the Java and C# versions have done against the simple mathserver example. Some of it might be down to my not figuring how the differences in the APIs are meant to work.

For py_interface, I had to comment out the line

[__import__(item) for item in __all__]

from init.py to get imports to work at all; and even then, the simple

from otp import *

def Handler(Result):
    print Result

cNode = erl_node.ErlNode("clientnode@chloe.ravnaandtines.com", erl_opts.ErlNodeOpts(cookie="cookie"))
print cNode
print cNode.Publish()
mBox = cNode.CreateMBox()
print mBox
mBox.SendRPC("servernode@chloe.ravnaandtines.com", 
    "mathserver", "add", [1, 2], Handler)
raw_input("wait")

just sits there; while the Ruby code

require 'erlang_node'
 
s_node = Erlang::Node.new("servernode@chloe.ravnaandtines.com")
c_node = Erlang::LocalNode.new("clientnode@chloe.ravnaandtines.com", "cookie")
connection = Erlang::Connection.new(s_node, c_node)
connection.sendRPC("mathserver", "add", [1,2])
sum = connection.receiveRPC()
puts "Fail" unless sum == 3

throws a different exception every time I run it, from some place or other inside the connection initializer.

So they both need deeper inspection than this simple kicking of the tyres, maybe modifying for R12 nodes, maybe just reverse engineering the kinks out of the driver programs.