environment.go

package main

type Environment struct {
	values    map[string]interface{}
	enclosing *Environment
}

func NewEnvironment(enclosing *Environment) *Environment {
	return &Environment{
		values:    map[string]interface{}{},
		enclosing: enclosing,
	}
}

func (e Environment) define(name string, value interface{}) {
	e.put(name, value)
}

func (e Environment) ancestor(distance int) Environment {
	environment := e
	for i := 0; i < distance; i++ {
		environment = *environment.enclosing
	}
	return environment
}

func (e Environment) get(name Token) interface{} {
	if elem, ok := e.values[name.lexeme]; ok {
		return elem
	}
	if e.enclosing != nil {
		return e.enclosing.get(name)
	}

	panic(NewRuntimeError(name, "undefined variable '"+name.lexeme+"'."))
}

func (e Environment) getAt(distance int, name string) interface{} {
	return e.ancestor(distance).values[name]
}

func (e Environment) assign(name Token, value interface{}) {
	if _, ok := e.values[name.lexeme]; ok {
		e.put(name.lexeme, value)
		return
	}
	if e.enclosing != nil {
		e.enclosing.assign(name, value)
		return
	}

	panic(NewRuntimeError(name, "undefined variable '"+name.lexeme+"'."))
}

func (e Environment) assignAt(distance int, name Token, value interface{}) {
	e.ancestor(distance).values[name.lexeme] = value
}

func (e Environment) put(name string, value interface{}) {
	e.values[name] = value
}