Calling Python from ECLiPSe

It is possible to call python function from ECLiPSe.

How to define a python function call it from ECLiPSe

The steps to achieve this are quite simple.

• Define a python function.
• Register it using function pyclp.addPythonFunction()
• Call from ECLiPSe with call_python_function predicate.

Python function definition

Python function tha implement the predicate shall have one argument. This argument will be used to pass a list of the term used in the invocation. Python function shall return the following values pyclp.SUCCEED or pyclp.FAIL any other values are equivalent to pyclp.FAIL It can be called in this function a pyclp.unify() to unify to term and interact with ECLiPSe term.

Example:

def py_unify(args):
   return pyclp.unify(args[0],args[1])

Register python function for calling

In order to be able to excute a python function from ECLiPSe it is required to register the function by calling pyclp.addPythonFunction() after having executed pyclp.init()

Example:

init()
pyclp.addPythonFunction("my_unify",py_unify)

Call python function from ECLiPSe

To excecute the python function from ECLiPSe use call_python_function predicate. This predicate is declared in pyclp module. This shall be imported in the user module. pyclp is created when pyclp.init() is executed and it is automatically imported in the eclipse module (the default one)

Example:

use_module pyclp call_python_function("my_unify",[A,B])

Modify ECLiPSe variables

In the python function it is possible to use all class to represent ECLiPSe object like: pyclp.Atom(), Compound() etc.. but not pyclp.resume(),:py:meth:pyclp.init, pyclp.cut() and pyclp.cleanup()

Handling python exceptions

Exception raised in the python function it is stored and reraised inside the pyclp.resume() function if a ECLiPSe signal python_error is not masked by ECLiPSe.

Internal sequence of operations:

python script          ECLiPSe                  user python function

resume()       ---->
                       call_python_function --->
                                                 raise exception
                                                 (exception stored)
                                                 signal event "python_error"
                                            <--
                       if not masked
                       send THROW to resume
               <----
 if the event
 is "python_error"
 restore exception
 and raise it.

Complete Example

Example:

from pyclp import *

def external_predicate(arguments):
   #arguments store all arguments passed with call_python_function
   #Note unify usage
   return unify(arguments[0],arguments[1])

init()   #Init ECLiPSe engine
#Register function with 'my_name' atom
add_python_function('my_name',external_predicate)
my_var=Var()
# call_python_function,'my_name',[1,My_var])
Compound('call_python_function',Atom('my_name'),[1,my_var]).post_goal()
resume()
if my_var.value() != 1:
   print("Failed resume ")

If an exception is raised during the python function execution abort event will be raised by ECLiPSe with the following message. If this event will be handled by the user in ECLiPSe program, ECLiPSe engine will send a message to python (FLUSHIO) and then THROW value. See the below example.