selsl/selsl/object.go

package selsl

import "fmt"

type Slots map[string]Object

func (s Slots) Set(name string, inst Object) Slots {
	s[name] = inst
	return s
}

func (s Slots) Get(name string) Object {
	res, ok := s[name]
	if !ok {
		return Nil
	}
	return res
}

/*
func (s Slots) Clone() Slots {
	clone := Slots{}
	for k, v := range s {
		clone[k] = v.Clone()
	}
	return clone
}
*/

// Constants for special object slot names
const (
	ParentSlot = "*parent"
	SelfSlot   = "*self"
	MeSlot     = "*me"
	ArgsSlot   = "*args"
)

// IsReturner is a marker interface for types that cause
// a return.
type IsReturner interface{ IsReturn() }

// Breaker is a marker interface for a type that cases
// a break in flow.
type IsBreaker interface{ IsBreak() }

// A Thrower is a marker interface for a type that causes
// a throw.
type IsThrower interface{ IsThrow() }

// Type is the type of an object. It is simply a string.
type Type string

// A message can be send to an object. It is also an object.
type Message struct {
	Name string
	Args []Object
	Env  Object
	Actor
}

func (m Message) String() string {
	return "message: " + m.Name
}

func (Message) Type() Type {
	return Type("message")
}

func (m Message) Value(env Object) Object {
	return m
}

func (m Message) Send(Message) Object {
	return m
}

// Object is the interface for all objects in SELSL.
type Object interface {
	// String stringifies the value of the object.
	String() string
	// Type returns the name of the type in lower case.
	Type() Type
	// Value evaluates the object in a context.
	Value(env Object) Object
	// Send sends a message to the object.
	Send(msg Message) Object
}

type NilObject struct{}

func (NilObject) String() string {
	return "nil"
}

func (NilObject) Value(env Object) Object {
	return nil
}

func (NilObject) Type() Type {
	return Type("nil")
}

func (NilObject) Send(Message) Object {
	return Nil
}

var Nil Object = NilObject{}

func ParentOf(val Object) Object {
	return val.Send(Message{Name: ParentSlot})
}

/*
type Environment struct {
	Instance
}

func NewEnvironment(parent, me, to Object, args ...Object) *Environment {
	name := "_env"
	if parent != nil {
		name = parent.Name() + "_env"
	}
	res := &Environment{Instance{name: name, slots: Slots{}}}
	res.Set(ParentSlot, parent)
	res.Set(SelfSlot, to)
	res.Set(ArgsSlot, List(args))
	res.Set(MeSlot, me)
	return res
}

func SendInEnv(to Object, message string, env Object) Object {
	lookup := to
	value := lookup.Slots().Get(message)
	for value == Nil {
		lookup = ParentOf(lookup)
		if lookup == Nil || lookup == nil {
			panic("Object does not support message " + message)
		}
		value = lookup.Slots().Get(message)
	}
	return value.Value(env)
}

func Send(to Object, message string, me, here Object, args ...Object) Object {
	env := NewEnvironment(here, me, to, args...)
	return SendInEnv(to, message, env)
}
*/

// Instance is a concrete implementation of Object
// which can be embedded into Go structs to help them
// become Objects themselves.
type Instance struct {
	// the type of the instance, used in Type()
	kind Type
	// Slots, used to store members
	slots Slots
}

// String stringifies the value of the instance.
func (i Instance) String() string {
	res := string(i.kind) + " { "
	for k, v := range i.slots {
		res += "\n" + k + ":" + v.String()
	}
	res += " } "
	return res
}

func (i Instance) Type() Type {
	return Type(i.kind)
}

func (i Instance) Value(env Object) Object {
	return i
}

func (i Instance) Send(message Message) Object {
	value := i.slots.Get(message.Name)
	if value == nil || value == Nil {
		// XXX should return an error in stead.
		return Nil
	}
	return value.Value(message.Env)
}

func (i *Instance) Set(name string, inst Object) *Instance {
	i.slots.Set(name, inst)
	return i
}

func NewInstance(kind string) *Instance {
	return &Instance{kind: Type(kind), slots: Slots{}}
}

// A primitive is a function implemented in Go that
// on evaluation as an Object calls that function
// with the given environment
type Primitive func(env Object) Object

func (p Primitive) Type() Type {
	return Type("primitive")
}

func (p Primitive) Send(m Message) Object {
	return p.Value(m)
}

func (p Primitive) Value(env Object) Object {
	return p(env)
}

func Self(o Object) Object {
	return o.Send(Message{Name: SelfSlot})
}

func Me(o Object) Object {
	return o.Send(Message{Name: MeSlot})
}

func Args(o Object) List {
	list := o.Send(Message{Name: ArgsSlot})
	if list == Nil {
		return List{}
	}
	return list.(List)
}

func Unary(unary func(target Object) Object) Primitive {
	return func(env Object) Object {
		return unary(Self(env))
	}
}

func Nullary(nullary func() Object) Primitive {
	return func(env Object) Object {
		return nullary()
	}
}

type String string

func (s String) String() string {
	return string(s)
}

func (s String) Type() Type {
	return Type("string")
}

func (p String) Send(m Message) Object {
	// XXX implement string methods here
	return Nil
}

func (s String) Value(env Object) Object {
	return s
}

type List []Object

func (l List) Type() Type {
	return Type("list")
}

func (l List) String() string {
	res := fmt.Sprintf("list: ")
	sep := ""
	for _, o := range l {
		res = fmt.Sprintf("%s %s %s", res, sep, o.String())
		sep = "and"
	}
	res += ";"
	return res
}

func (l List) Send(m Message) Object {
	// XXX implement list methods here
	return Nil
}

func (l List) Value(env Object) Object {
	return l
}

type Error struct {
	*Instance
	Error error
}

func (e Error) String() string {
	return fmt.Sprintf("error `%s`", e.Error)
}

func (e Error) Value(env Object) Object {
	return e
}

func NewErrorBasic(err error) Error {
	return Error{Instance: NewInstance("error"), Error: err}
}

func NewError(err string) Error {
	return NewErrorBasic(fmt.Errorf("%s", err))
}

type Int struct {
	*Instance
	Int int64
}

func NewInt(i int64) Int {
	return Int{Instance: NewInstance("int"), Int: i}
}

func (i Int) String() string {
	return fmt.Sprintf("%d", i.Int)
}

func (i Int) Value(env Object) Object {
	return i
}

type Statement struct {
	*Instance
	Command Object
	Param   List
}

func (s Statement) String() string {
	return fmt.Sprintf("%s %s.", s.Command.String(), s.Param.String())
}

/*
func (s Statement) Value(env Object) Object {
	cenv := env
	cenv.Slots().Set(ArgsSlot, s.Param)
	return SendInEnv(env, s.Command.Name(), cenv)
}*/

var _ Object = Error{}
var _ Object = String("")
var _ Object = Int{}
var _ Object = List{}