Add variable bindings and references to the evaluator.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/object/environment.go

@@ -0,0 +1,19 @@
+package object
+
+func NewEnvironment() *Environment {
+	return &Environment{store: map[string]Object{}}
+}
+
+type Environment struct {
+	store map[string]Object
+}
+
+func (e *Environment) Get(name string) (Object, bool) {
+	obj, ok := e.store[name]
+	return obj, ok
+}
+
+func (e *Environment) Set(name string, obj Object) Object {
+	e.store[name] = obj
+	return obj
+}