Implemented Value interface

src/core/EvaluateCall.go

@@ -11,16 +11,15 @@ func (f *Function) EvaluateCall(expr *expression.Expression) (eval.Value, error)
 	types, err := f.CompileCall(expr)
 
 	if err != nil {
-		return eval.Value{}, err
+		return nil, err
 	}
 
 	if len(types) == 0 {
-		return eval.Value{}, errors.New(errors.UntypedExpression, f.File, expr.Token.Position)
+		return nil, errors.New(errors.UntypedExpression, f.File, expr.Token.Position)
 	}
 
-	value := eval.Value{
-		Kind:     eval.Register,
-		Type:     types[0],
+	value := eval.Register{
+		Typ:      types[0],
 		Register: f.CPU.Output[0],
 	}