ExiL

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What's this?

ExiL (Expert System in Lisp) is a CLIPS-based expert system building tool written in Common Lisp, with forward chainging and a very basic backward chaining inference engine. It was developed along my computer science master's thesis and is meant for academic purposes, not for real-case scenerios (at least yet).

Supported LISP implementations

I've developed ExiL using SBCL 1.1.13 (SLIME and Emacs), so that's where it runs best. I've also tested it in LispWorks™ Personal Edition 6.1.1, for which I've also created a very basic GUI.

Usage

In sbcl load the file load.lisp, enter the exil-user package and you can start using the front-end macros. In LispWorks loading using quicklisp/ASDF doesn't work - my custom destructuring macros don't get expanded, so just use load-manual.lisp, which compiles and loads each file in turn, avoiding ASDF.

Documentation

• CLIPS documentation - http://clipsrules.sourceforge.net/OnlineDocs.html
• API reference - https://github.com/Incanus3/ExiL/wiki/API-reference
• more extensive documentation is part of the text part of the thesis (text/diplomka.pdf), unfortunately it's in Czech

Examples

• ordered facts - https://github.com/Incanus3/ExiL/blob/master/src/examples/examples-simple.lisp
• templated facts - https://github.com/Incanus3/ExiL/blob/master/src/examples/examples-template.lisp
• templated facts using CLIPS syntax - https://github.com/Incanus3/ExiL/blob/master/src/examples/examples-clips.lisp

Used tools

• CLIPS - http://clipsrules.sourceforge.net/
  expert system building tool

• ASDF (Another System Definition Facility) - http://common-lisp.net/project/asdf/
  project definition and loading facility (alternative to LispWorks defsystem)

• quicklisp - http://www.quicklisp.org/beta/
  library manager for CL

• iterate - http://common-lisp.net/project/iterate/
  extensible loop alternative with more lispy syntax

• xlunit - http://quickdocs.org/xlunit/
  CLOS based unit testing framework for CL

• sbcl - http://www.sbcl.org/
  open source high performance Common Lisp compiler

• LispWorks™ - http://www.lispworks.com/
  integrated cross-platform development tool for ANSI Common Lisp

• git - http://git-scm.com/
  open source distributed version control system

What is implemented

• basic fact manipulation - (assert), (retract)
  • retract accepts integers (as CLIPS) or fact specifiers, can be even mixed
  • TODO: document symbols and values usable in facts (CLIPS ug page 8)
  • TODO: document case sensitivity and other equivalence issues
• structured (unordered, templated) facts
  • (modify)
  • clips and lispy syntax for template and structured fact definition and modify
• facts listing - (facts)
• fact group definition - (deffacts) + (reset), (undeffacts)
• environment cleanup
  • (clear) - clears facts, agenda, undo/redo stacks, (goals, backtracking stack - backward chaining)
  • (reset) - (clear) + activate fact groups
  • (complete-reset) - clears all slots - including templates, fact groups, rules
• watchers - (watch facts), (watch rules), (watch activations), (watch all)
• rules
  • (defrule) - both syntaxes for condition specifiers
  • activations can be any lisp expressions, but beware! they're EVALuated - so they don't see lexical scope
  • (ppdefrule)
• agenda listing - (agenda)
• forward chaining inference execution - (run), (step), (halt)
• backward chaining inference execution - (defgoal goal-spec), (goals), (back-run), (back-step)
• functional alternatives - macros taking unquoted names or expressions have functional counterparts suffixed by 'f', which can be used by other code to call ExiL functionality

What isn't implemented

• multislot templates
• template slot types
• function calls in (assert), (retract) aren't evaluated, not even in rule's activations
  • but this can be done using assertf, retractf, ...
• advanced rule syntax:
  • wildcards - $?
  • field constraints - ~, |, &
  • test predicate in rule conditions
  • =( directive in rules
  • (undefrule *) - wildcard
• only basic strategies implemented
  • new strategies can be defined, but this requires accessing the internal rule representation, so it's not very useful at the moment
• state saving and loading - program can be easily saved and loaded by interpreter
• CLIPS string, printing, integer, ... functions - use lisp ones instead
• CLIPS deffunction - use lisp
• rule salience
• incremental reset, refresh
• batch, system
• dribbling
• brakepoints
• (matches)
• CLIPS objects, classes, messages
• didn't care about performance, LispWorks personal edition stack overflows easily