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Erlang Language Integrated Production System (ELIPS) library.

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README.md

Erlang Language Integrated Production System (ELIPS).

Intro

This library is a tool to create a reactive rule based agents. The rules of behavior of an agent specified via a special function handle_pattern/3, where each clause declare one rule. Each such clause have its Left Hand Side (LHS) which is a pattern specification and Right Hand Side (RHS) which define a reaction. LHS in its turn consists of pattern itself and guards. Pattern is a list of term (fact) patterns. RHS is an ordinary Erlang code optionally returning a set of asserts or retires. Example: TBD

Background

The name of this library and basic concept inspired by CLIPS (http://clipsrules.sourceforge.net/), nevertheless, at the current state ELIPS have a different ideology than CLIPS and probably could not be compared directly (e.g. like JESS and CLIPS). ELIPS is a really integrated to an Erlang language. In contrast with CLIPS, ELIPS have no its own language to represent rules but it successfully uses the Erlang language itself slightly changing (augmenting) semantics of pattern matching, fortunately Erlang already pattern matching language. And fortunately Erlang have a "parse transform" mechanism to be able to hack a language:)

Design & implementation notes

This library allows to create a so called ELIPS agents. One such an agent is represented by its module which is a callback module for an ELIPS behavior. Also, such a module must use parse transform to be augmented with a couple of functions generated as a result of analysis of rules declared in an agent module. At runtime this module is plugged into a special host process (see elips.erl). This process is capable to accept a messages (or events if you want). The accepted messages are translated to an operations like assert and retire. These operations modify a working memory of an agent. Working memory implemented using a core Erlang module ets. Each agent process have its separated ets based working memory. When working memory accumulates a data that matches some rule the rule is activated and RHS is executed.

Usage

Integrate library to your project

This is a rebar'ized project, so, if you are already using rebar, just insert a reference to this git repo at your rebar.config. Otherwise clone this repo, and run erl -make. To compile your project, ELIPS library must be on ERL_LIBS to compile your agents or use -pa for erlc:

  • env ERL_LIBS=path/to/the/elips erlc my_proj/src/myagent.erl
  • erlc -pa path/to/the/elips/ebin my_proj/src/myagent.erl

Implementing your own agent

To create your own ELIPS agent you must create a module say myagent. This module MUST have a set of functions satisfying to some conventions. In Erlang world we say that it is a callback module implementing a behavior elips. Also, module myagent must use a special parse transform to be augmented with auto generated hidden functions. On practice you must follow these steps:

  • first of all insert in myagent directive -include_lib("elips/include/elips.hrl").
  • implement functions:
    • init/1 - initialize a state of an agent and working memory (WM)
    • handle_event/3 - accepts an event sent with elips:notify/2 optionally changes the state and WM
    • handle_info/2 - similar to handle_event/3 but it accepts a system messages and those sent not with elips:notify/2
    • handle_pattern/3 - handles a patterns matched against WM i.e. it may be considered as a set of rules
    • terminate/3 - handles a termination of an agent process
    • code_change/3 - handles an event of code change

To run an agent it is enough to say something like elips:start(myagent_1,myagent,[],[]). Copy a examples/elips_skeleton.erl and rename to your_agent_module.erl to implement a new agent.

Runtime

After you perform elips:start(myagent_1,myagent,[],[]) the new process is created and registered with name myagent_1 and initialized with myagent. This process ready to accept events and handle them using myagent callback module. To send events use elips:notify(myagent_1, {some_event, with, some, params}). It is quite similar to standard OTP behavior gen_event. So, each agent is a separate Erlang process.

Examples

TBD

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