CLIPSgo Golang Bindings

A Go wrapper for CLIPS, inspired by clipspy and implemented using cgo.

Design

CLIPSgo attempts to follow closely the model defined by clipspy. Anyone familiar with clipspy should find clipsgo fairly straightforward to understand. That said there are a few notable areas of differences.

• Because Go is type safe, some APIs work differently out of necessity
• clipsgo adds a SendCommand call inspired by pyclips, enabling an interactive shell.
• clipsgo includes a Shell() API call based on this that opens an interactive shell, and includes readline-style history and syntax highlighting
• clipsgo builds into an executable that simply acts as an interactive CLIPS shell

Interactive use

You may run clipsgo directly in order to use an interactive shell.

Also, in your clipsgo-based programs, you may set up an environment that includes Go-based functions and / or is preloaded with data, then open an interactive session within that environment.

func main() {
	env := clips.CreateEnvironment()
	// ... modify to your liking
	env.Shell()
}

Data Types

CLIPS data types are mapped to GO types as follows

CLIPS	Go
INTEGER	int64
FLOAT	float64
STRING	string
SYMBOL	clips.Symbol
MULTIFIELD	[]interface{}
FACT_ADDRESS	clips.Fact
INSTANCE_NAME	clips.InstanceName
INSTANCE_ADDRESS	clips.Instance
EXTERNAL_ADDRESS	unsafe.Pointer

Basic Data Abstractions

For detailed information about CLIPS see the CLIPS documentation

While most of the CLIPS documentation starts from facts and templates, given that you'll be programming Go I recommend that you build your rules and "facts" based on classes and instances, instead of templates and facts. Everything you can do with facts, you can do with instances, but the reverse is not true. Any Go programmer is likely to be familiar with the object oriented concepts of CLIPS Object Oriented Language (COOL) and in fact may find them more familiar and comfortable than the older, more procedural base language.

Instances

Instances are instantiations of specific classes. They store values by name, similar to Go maps. They also support inheritance and instance methods using message sending.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

err := env.Build(`(defclass Foo (is-a USER)
        (slot bar
            (type INTEGER))
        (multislot baz)
)`)
assert.NilError(t, err)
err := env.Build(`(defmessage-handler Foo handler ()
        (printout t "bar=" ?self:bar crlf)
)`)
assert.NilError(t, err)

inst, err := env.MakeInstance(`(of Foo (bar 12))`)
assert.NilError(t, err)

ret, err := inst.Slot("bar")
assert.NilError(t, err)
assert.Equal(t, ret, int64(12))

ret := inst.Send("handler", "")

Insert

A user-defined struct may be "inserted" as a class and / or instance in CLIPS. The term "Insert" is taken from DROOLS, although unlike DROOLS no long-term link between the user struct and the CLIPS instance is retained. The data is simply copied in.

A nil pointer to a struct type is sufficient to insert a class. Inserting a class will result in building a defclass construct in CLIPS that represents the fields of the struct. If the struct contains structs, or pointers to structs, these will become slots of type INSTANCE-NAME, and the struct that is referred will also be inserted.

type ChildClass struct {
    Intval   *int
    Floatval *float64
}
type ParentClass struct {
    Str   string
    Child ChildClass
}
var template *ParentClass

cls, err := env.InsertClass(template)
assert.NilError(t, err)
assert.Equal(t, cls.String(), `(defclass MAIN::ParentClass
   (is-a USER)
   (slot Str
      (type STRING))
   (slot Child
      (type INSTANCE-NAME)
      (allowed-classes ChildClass)))`)

When an instance is inserted, a class for that data type will implicitly be inserted if no class by that name already exists. If a class already exists, it will be used as-is (and may not match the fields of the given data, causing an error, if it was created by some other means.)

type ChildClass struct {
    Intval   *int
    Floatval *float64
}
type ParentClass struct {
    Str   string
    Child ChildClass
}
intval := 99
floatval := 107.0
template := ParentClass{
    Str: "with actual value",
    Child: ChildClass{
        Intval:   &intval,
        Floatval: &floatval,
    },
}

inst, err := env.Insert("", template)
assert.NilError(t, err)
assert.Equal(t, inst.String(), `[gen1] of ParentClass (Str "with actual value") (Child [gen2])`)

subinst, err := env.FindInstance("gen2", "")
assert.NilError(t, err)
assert.Equal(t, subinst.String(), `[gen2] of ChildClass (Intval 99) (Floatval 107.0)`)

Extract

An instance can also be "extracted" as either a struct or a map. This functionality is somewhat analogous to json.Unmarshal. The caller supplies an object which will be filled in by clipsgo.

Matching the name of the struct field to the slot name is determined by the following rules:

• If the struct field has a "clips" tag, that tag is used as the slot nam.
• Otherwise, if the struct has a "json" tag, that tag is used.
• Otherwise the field name of the struct is used

Note that instances are extracted recursively; if a slot in the instance is an INSTANCE-ADDRESS or INSTANCE-NAME, the referred instance will also be extracted as structured data

err := env.Build(`(defclass Foo (is-a USER)
    (slot Int (type INTEGER))
    (slot Float (type FLOAT))
    (slot Sym (type SYMBOL))
    (multislot MS))
`)
assert.NilError(t, err)

inst, err := env.MakeInstance(`(of Foo (Int 12) (Float 28.0) (Sym bar) (MS a b c))`)
assert.NilError(t, err)

type Foo struct {
    IntVal    int     `json:"Int"`
    FloatVal  float64 `clips:"Float"`
    Sym       Symbol
    MultiSlot *[]interface{} `json:"MS,omitempty"`
}

var retval Foo
err = inst.Extract(&retval)

output := Foo{
    IntVal:   12,
    FloatVal: 28.0,
    Sym:      Symbol("bar"),
    MultiSlot: &[]interface{}{
        Symbol("a"),
        Symbol("b"),
        Symbol("c"),
    },
}

assert.DeepEqual(t, retval, output)

Facts

A fact is a list of atomic values that are either referenced positionally, for "ordered" or "implied" facts, or by name for "unordered" or "template" facts.

Ordered Facts

Ordered Facts represent information as a list of elements. There is no explicit template for an ordered fact, but they do have an implied template. A reference to the implied template of an ordered fact can be obtained, and can be used to programmatically assert ordered facts.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

fact, err := env.AssertString(`(foo a b c)`)
defer fact.Drop()

tmpl := fact.Template()
assert.Assert(t, tmpl.Implied())
fact, err = tmpl.NewFact()

ifact, ok := fact.(*ImpliedFact)
assert.Assert(t, ok)

ifact.Append("a")
ifact.Extend([]interface{}{
    Symbol("b"),
    3,
})

ifact.Set(2, "c")
ifact.Assert()

Similar to instances, an ordered fact may be extracted to a user-provided structure. Extracted ordered facts will translate to a slice of interface. The user may use a more specific slice, in which case the slice will be automatically converted (if possible - note that an unordered fact need not have all values of the same type, which would likely lead to errors.)

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

fact, err := env.AssertString(`(foo a b c)`)
defer fact.Drop()

var strslice []string
err = fact.Extract(&strslice)
assert.Equal(t, strslice, []string {
    "a", "b", "c",
})

Template Facts

Unordered facts represent data similar to Go maps. They require a template to be defined, which provides a formal definition for what data is represented by the fact.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

env.Build("(deftemplate foo (slot bar) (multislot baz))")

tmpl, err := env.FindTemplate("foo")
assert.NilError(t, err)
fact, err := tmpl.NewFact()
assert.NilError(t, err)

tfact, ok := fact.(*TemplateFact)
assert.Assert(t, ok)

tfact.Set("bar", 4)
tfact.Set("baz", []interface{}{
    Symbol("b"),
    3,
})
ifact.Assert()

Template facts may be extracted to structs or to a map

var mapvar map[string]interface{}
err = fact.Extract(&mapvar)
assert.NilError(t, err)
assert.DeepEqual(t, mapvar, map[string]interface{}{
    "bar": int64(4),
    "baz": []interface{} {
        Symbol("b"),
        3,
    },
})

Evaluating CLIPS code

It is possible to evaluate CLIPS statements, retrieving their results in Go.

Eval

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

ret, err := env.Eval("(create$ foo bar baz)")

Note that this functionality relies on CLIPS eval function, which does not accept aribtrary commands. It does not allow CLIPS constructs to be created for example - for that you need env.Build(). It also does not allow facts to be asserted - use env.AssertString()

The return from Eval is interface{}, since it is not possible to know in advance what kind of data will be returned.

For cases where the user is able to know an expected return type, an ExtractEval function is provided. This will marshall the returned data into an object provided by the user. Using ExtractEval can reduce the amount of boilerplate type checking required. Type conversions are applied as necessary. An error will be generated if a numeric type conversion results in loss of precision.

intval := 4
err = env.ExtractEval(&intval, "12")
assert.NilError(t, err)
assert.Equal(t, intval, 12)

sliceval := make([]string, 0)
err = env.ExtractEval(sliceval, "(create$ a b c d e f)")
assert.NilError(t, err)
assert.DeepEqual(t, sliceval, []string{
    "a",
    "b",
    "c",
    "d",
    "e",
    "f",
})

var factval Fact
ret, err := env.ExtractEval(&factval, "(bind ?ret (assert (foo a b c)))")
assert.NilError(t, err)
assert.Equal(t, factval.String(), "(foo a b c)")

SendCommand

In order to overcome some of the limitations of the CLIPS eval command, clipsgo provides a higher-level function called SendCommand which accepts any arbitrary CLIPS command.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

// try some stuff that Eval chokes on
err := env.SendCommand("(assert (foo a b c))")
assert.NilError(t, err)

This avoids the need to know in advance which call to make. On the other hand, no return value is provided; SendCommand is primarily intended for more interactive evaluation of unpredictable input.

Defining CLIPS Constructs

CLIPS constructs must be defined in CLIPS language. Use the Load() or Build() functions to define them.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

err := env.Build(`
(defrule my-rule
    (my-fact first-slot)
=>
    (printout t "My Rule fired!" crlf)
)`)
assert.NilError(t, err)

Embedding Go

The DefineFunction() method allows binding a Go function within the CLIPS environment. It will be callable from within CLIPS using the given name as though it had been defined with the deffunction construct.

Clipsgo will attempt to marshall functions passed from CLIPS to the correct types to match the function. If it cannot, CLIPS will error on the attempted function call.

Each argument must be one of types listed as equivalent to one of the CLIPS data types, with one notable exception - it is acceptable to use lower-scale types like int, int8, or float32. Clipsgo will automatically convert, or will return an error if the number is too large for the conversion.

Any number of return values is supported. If the last return value of the funciton is an error type, clipsgo will interpret it as an error and not include it in the function return values. A single non-error value will be returned directly, more than that will return a multifield.

Variadic functions are also supported.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

callback := func(foo int, bar float64,
                multifield []interface{},
                vals ...clips.Symbol) (bool, error)
    return true, nil
}

err := env.DefineFunction("test-callback", callback)
assert.NilError(t, err)

_, err = env.Eval("(test-callback 1 17.0 (create$ a b c) a b c d e f)")
assert.NilError(t, err)

Go Reference Objects Lifecycle

All of the Go objects created to interact with the CLIPS environment are simple references to the CLIPS data structure. This means that interactions with the CLIPS shell can cause them to become invalid. In most cases, deleting or undefining an object makes any Go reference to it unusable.

import (
    "github.com/keysight/clipsgo/pkg/clips"
)

env := clips.CreateEnvironment()
defer env.Delete()

templates := env.Templates()
env.Clear() // From here, all templates are gone so all references are unusable

// this will cause an error
for _, tmpl := range templates {
    fmt.Printf("%v\n", tmpl)
}

Building From Sources

The build requires the CLIPS source code to be available, and to be built into a shared library. The provided Makefile makes this simple.

$ make

There are also targets for test and coverage to run the test suite.

Once CLIPS is built and available, subsequent builds can be done with a simple go build.

Reference documentation

The code has Godoc throughout. To view them, run

$ godoc -http=:6060

Then access http://localhost:6060/ from your browser