muesli/value.go

package muesli

import "fmt"

/* Run time values */
type Value interface {
	String() string
	Type() TypeValue
	// Convert the value to a normal go value which must be passed 
	// in as a pointer to which the value mmust be set, 
	// or return an error if the concversion is not possible.
	Convert(to interface{}) error
}

type IntValue int64
type FloatValue float64
type StringValue string
type BoolValue bool
type WordValue string
type TypeValue string

type ErrorValue struct {
	error
}

type EmptyValue struct {
}

type ListValue struct {
	List []Value
}

// Values is simply a shorthand alias for []Value
type Values = []Value

const (
	TrueValue       = BoolValue(true)
	FalseValue      = BoolValue(false)
	IntTypeValue    = TypeValue("Int")
	FloatTypeValue  = TypeValue("Float")
	StringTypeValue = TypeValue("String")
	BoolTypeValue   = TypeValue("Bool")
	WordTypeValue   = TypeValue("Word")
	ErrorTypeValue  = TypeValue("Error")
	TypeTypeValue   = TypeValue("Type")
	EmptyTypeValue  = TypeValue("Empty")
	ListTypeValue   = TypeValue("List")
	AnyTypeValue    = TypeValue("Any")
)

var NilValue = Value(nil)

func (val IntValue) String() string {
	return fmt.Sprintf("%d", int64(val))
}

func (val FloatValue) String() string {
	return fmt.Sprintf("%f", float64(val))
}

func (val BoolValue) String() string {
	if bool(val) {
		return "true"
	} else {
		return "false"
	}
}

func (val StringValue) String() string {
	return string(val)
}

func (val WordValue) String() string {
	return string(val)
}

func (val TypeValue) String() string {
	return string(val)
}

func (val ErrorValue) String() string {
	return fmt.Sprintf("%s", val.Error())
}

func (val EmptyValue) String() string {
	return "<empty>"
}

func (val ListValue) String() string {
	res := "["
	sep := ""
	for _, elt := range val.List {
		res = res + sep + elt.String()
		sep = ", "
	}
	res += "]"
	return res
}

func (v IntValue) Type() TypeValue    { return IntTypeValue }
func (v FloatValue) Type() TypeValue  { return FloatTypeValue }
func (v StringValue) Type() TypeValue { return StringTypeValue }
func (v BoolValue) Type() TypeValue   { return BoolTypeValue }
func (v WordValue) Type() TypeValue   { return WordTypeValue }
func (v TypeValue) Type() TypeValue   { return TypeTypeValue }
func (v ErrorValue) Type() TypeValue  { return ErrorTypeValue }
func (v EmptyValue) Type() TypeValue  { return EmptyTypeValue }
func (v ListValue) Type() TypeValue   { return ListTypeValue }

func NewErrorValuef(format string, args ...interface{}) ErrorValue {
	err := fmt.Errorf(format, args...)
	return ErrorValue{err}
}

func NewListValue(elements ...Value) ListValue {
	return ListValue{elements}
}

func (list *ListValue) Append(elements ...Value) {
	list.List = append(list.List, elements...)
}

func (list *ListValue) AppendList(toAppend ListValue) {
	list.List = append(list.List, toAppend.List...)
}

func (list ListValue) Length() int {
	return len(list.List)
}

func (list *ListValue) Index(i int) Value {
	if i >= len(list.List) {
		return NilValue
	}
	return list.List[i]
}


func (list *ListValue) First() Value {
	return list.Index(0)
}

func (list *ListValue) Last() Value {
	return list.Index(list.Length()-1)
}


func EmptyListValue() ListValue {
	return ListValue{make([]Value, 0)}
}

func EmptyValueArray() []Value {
	return make([]Value, 0)
}

func NewValueArray(elements ...Value) []Value {
	return elements
}


func (from IntValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		case *int8:
			(*toPtr) = int8(from)
		case *int16:
			(*toPtr) = int16(from)
		case *int32:
			(*toPtr) = int32(from)
		case *int64:
			(*toPtr) = int64(from)
		case *int:
			(*toPtr) = int(from)
		case *bool:			 
			(*toPtr) = (from != 0)
		case *float32:
			(*toPtr) = float32(from)
		case *float64:
			(*toPtr) = float64(from)
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}

func (from FloatValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		case *int8:
			(*toPtr) = int8(from)
		case *int16:
			(*toPtr) = int16(from)
		case *int32:
			(*toPtr) = int32(from)
		case *int64:
			(*toPtr) = int64(from)
		case *int:
			(*toPtr) = int(from)
		case *bool:			 
			(*toPtr) = (from != 0) 		
		case *float32:
			(*toPtr) = float32(from)
		case *float64:
			(*toPtr) = float64(from)
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}
	
func (from StringValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}

func (from WordValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}


func (from TypeValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}


func (from BoolValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *bool:			 
			(*toPtr) = bool(from) 		
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}

func (from ErrorValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *string:
			(*toPtr) = from.String()
		case *error:
			(*toPtr) = from.error
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}

func (from EmptyValue) Convert(to interface{}) error {
	return NewErrorValuef("Cannot convert the empty value %v to %v", from, to)
}

func (from ListValue) Convert(to interface{}) error {
	switch toPtr := to.(type) {
		case *[]Value:
			(*toPtr) = from.List
		default:
			return NewErrorValuef("Cannot convert value %v to %v", from, to)
	}
	return nil
}


/* Helpers to easily convert Muesli values to "normal" Go values. */
func From(from Value, to interface{}) error {
	return from.Convert(to)
}

/* Helpers to easily convert Muesli value lists to "normal" Go values. */
func ParseArgs(args []Value, to...interface{}) ([]interface{}, error) {
	if len(to) > len(args) {
		return nil, NewErrorValuef("Too few arguments, expected %d, got %d", len(to), len(args))
	}
	i:= 0
	for ; i < len(to) ; i ++ {
		fromElt := args[i]
		toElt 	:= to[i]
		err := fromElt.Convert(toElt)
		if err != nil {
			return nil, err
		}
	}
	rest := args[i:len(args)]
	return ListFromList(rest), nil
}

/* Helpers to easily convert Muesli values from "normal" Go values. */
func To(from interface{}) Value {
	switch val := from.(type) {
	case string:
		return StringValue(val)
	case int8:
		return IntValue(val)
	case int16:
		return IntValue(val)
	case int32:
		return IntValue(val)
	case int64:
		return IntValue(val)
	case int:
		return IntValue(val)
	case bool:
		return BoolValue(val)
	case float32:
		return FloatValue(val)
	case float64:
		return FloatValue(val)
	case error:
		return ErrorValue{val}
	case Value:
		return val
	default:
		return NewErrorValuef("Cannot convert value %v", from)
	}
}

func ListTo(froms ...interface{}) []Value {
	list := make([]Value, 0)
	for _, from := range froms {
		val := To(from)
		list = append(list, val)
	}
	return list
}

func ListFrom(froms []Value, tos ...interface{}) error {
	for i, from := range froms {
		if i >= len(tos) {
			break
		}
		err := From(from, tos[i])
		if err != nil {
			return err
		}
	}
	return nil
}

func ListFromList(froms []Value) []interface{} {
	res := make([]interface{}, len(froms))
	for i, from := range froms {
		res[i] = from
	}
	return res
}