We formally specified the type system and operational semantics of Loopω with Ott and Isabelle/HOL proof assistant. Moreover, both the type system and the semantics of Loopω have been tested using Isabelle/HOL program extraction facility for inductively defined relations. In particular, the program that computes the Ackermann function type checks and behaves as expected. The main difference (apart from the choice of an Ada-like concrete syntax) with Loopω comes from the treatment of parameter passing. Indeed, since Ott does not currently fully support α-conversion, we rephrased the operational semantics with explicit aliasing in order to implement the out parameter passing mode.